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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

The composition of the structure consists of a series of five concentric polyhedra comprising Cu(i) atoms, along with an additional set of five concentric polyhedra composed of ligands spanning a distance of 2 nm.

DOI： 10.1039/d3cc01811c

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpclett.2c02568

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Numerous reports hitherto show that the photoluminescence (PL) properties of metal nanoclusters (NCs) can be enhanced by alloying the metal cores. In particular, biicosahedral [AgxAu25-x(PPh3)(10)(SR)(5)Cl-2](2+) (abbreviated as AgxAu25-x hereafter; with PPh3 = triphenylphosphine; SR = thiolate ligand) NCs attract significant attention because their PL quantum yield is improved by 200 times when 13 Au atoms are replaced with Ag atoms (x = 13). In this contribution, the origin of the PL in the AgxAu25-x system and its remarkable enhancement are investigated on the basis of spectroscopic investigations of the PL behavior and its quenching by an organic fluorophore, finding that (i) the observed PL of AgxAu25-x is phosphorescent; (ii) not only Ag13Au12 but also Ag12Au13 NCs contribute to the PL; and (iii) replacing the central vertex atom of the biicosahedron with an Ag atom causes a blue shift of the triplet states, which suppresses the T-1-S-0 intersystem crossing and enhances the phosphorescence emission. Additionally, the results of single-particle PL spectroscopy and defocused imaging with rotation of linearly polarized excitation light reveal that the phosphorescence transition dipole moment of Ag13Au12 exists in the long axis direction of the biicosahedron. Furthermore, the AgxAu25-x NCs can sensitize molecular triplets and efficiently induce red-to-blue photon upconversion via triplet-triplet annihilation.

DOI： 10.1002/adom.202200864

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

In photoluminescence (PL) quenching and triplet fusion upconversion experiments with fluorescent organic-molecule quenchers, it was revealed that a rod-shaped, phosphine- and thiolate-protected biicosahedral Au-25 cluster (a representative di-superatomic molecule) exhibits only phosphorescence, not fluorescence, at room temperature with an intersystem crossing quantum yield of almost 100%. By virtue of these photophysical properties, this cluster can be used as a triplet sensitizer that undergoes direct singlet-triplet transitions in the near-infrared (NIR) region (730-900 nm), inducing photon upconversion from NIR to visible light.

DOI： 10.1039/d2nr00813k

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Ligand-protected Au₂Cu₆ cluster exhibits not only fluorescence but also phosphorescence at room temperature and serves as a triplet sensitizer in triplet fusion upconversion.

DOI： 10.1039/d1tc04591a

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Excited-state symmetry breaking (ESB) has attracted much attention because it is often observed in symmetric multipolar chromophores designed as two-photon absorption/emission materials. Herein, we report an ensemble and single-molecule fluorescence imaging and spectroscopy investigation of ESB in hexakis[4-(p-dioctylaminostyryl)phenylethynyl]benzene-(DB6), a two-photon absorber possessing a C-6-symmetric pi-D-6 structure (pi = hexaethynylbenzene, D = (p-dioctylaminostyryl)-phenyl group) consisting of three equivalent D-pi-D moieties. Ensemble and single- molecule measurements and theoretical calculations revealed that DB6 undergoes a photoabsorption process with two orthogonal transition dipole moments, whereas it fluoresces with a single transition dipole moment after one- or two-step ESB upon photoexcitation, depending on the environmental polarity. In nonpolar solvents and polymer films, one of the three D-pi-D sites becomes planar, and the excited state is localized on this moiety: a [D delta+-pi(delta-)-D delta+]* quadrupolar state is formed. In polar solvents, the symmetry is further broken within the planarized D-pi-D moiety, and the excited state is localized on one of the two D-pi sites; i.e., a D-[pi(delta-)-D delta+]* dipolar state is generated. Hence, DB6 can behave like a multichromophore with multiple emission sites in the molecule, which was demonstrated by stepwise photobleaching under photon antibunching conditions.

DOI： 10.1021/acs.jpcb.1c04915

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Two starburst-shaped organic chromophores, incorporating a hexaethynylbenzene core modified by five donor branches (D-branches) of (p-dioctylaminostyryl)benzene and one acceptor/anchoring branch (A-branch) of either carboxylic acid-terminated phenylethynylbenzene (SB-07) or cyanoacrylic acid-terminated diketopyrrolopyrrole (DPP)-thiophene (SB-08), were synthesized and applied to dye-sensitized solar cells (DSSCs). In these chromophores, the common donor moiety, five (p-dioctylaminostyryl)phenyl groups, exhibits excellent optical absorption in the visible region (molar absorption coefficient epsilon > 10(5) M-1 cm(-1) below 500 nm). The A-branch of SB-07 does not possess strong electron-accepting properties; however, the A-branch of SB-08, the DPP-thiophene moiety, serves as a strong electron acceptor site. Furthermore, the intramolecular charge-transfer (ICT) transition between the thiophene and DPP moieties extends the optical absorption range to the near-infrared region (similar to 800 nm). Optimized DSSC devices using SB-08 with coadsorption of chenodeoxycholic acid, in conjunction with iodide/triiodide-based electrolytes, exhibited incident photon-to-current conversion efficiency (IPCE) exceeding 70% in the 370-700 nm range and over 20% even at 800 nm, with a short-circuit photocurrent density (J(sc)) of 19.3 mA cm(-2) and a power conversion efficiency (PCE) of 6.4% under AM 1.5G illumination (100 mW cm(-2)). These results are considerably better than those of SB-07 (J(sc) = 7.0 mA cm(-2), PCE = 3.3%). The starburst-shaped architecture presented here can be used as a novel structural motif for metal-free organic sensitizers because it enables flexible modification of the multiple D-branches that enhance light-harvesting ability and the A-branch that serves as an excited electron transport pathway.

DOI： 10.1021/acsami.1c08431

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Photon upconversion (UC) from near-infrared (NIR) to visible has been realized using singlet-to-triplet absorption of sensitizers, which are currently limited to osmium complexes and semiconductor nanocrystals. Motivated by the atomically precise tunability of electronic structure and photophysical properties of noble metal clusters, which often possess absorption bands that extend into the NIR region, we investigated MAg24(SR)(18) (M=Ag, Pt; SR=2,4-dimethylbenzenethiolate) clusters as a new NIR-absorbing sensitizer for triplet-triplet annihilation UC. Combined with a blue light emitter, the NIR excitation (lambda(ex)=785 nm) of Ag-25(SR)(18) results in no UC emission, while PtAg24(SR)(18) exhibits strong UC emission. This enhancement is primarily due to a significant increase in the intersystem crossing quantum yield of the cluster associated with the spin-orbit coupling enhancement in the M@Ag-12 core.

DOI： 10.1002/anie.202013725

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/anie.202012120

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.202012120

Publisher：Wiley  

<jats:title>Abstract</jats:title><jats:p>The synthesis of a cyclohexa‐2,7‐(4,5‐diaryl)anthrylene ethynylene (<jats:bold>1</jats:bold>) was achieved for the first time by using 1,8‐diaryl‐3,6‐diborylanthracene and 1,8‐diaryl‐3,6‐diiodoanthracene as key synthetic intermediates. Macrocycle <jats:bold>1</jats:bold> possesses a planar conformation of approximately <jats:italic>D</jats:italic><jats:sub>6<jats:italic>h</jats:italic></jats:sub> symmetry, because of the triple‐bond linker between the anthracene units at the 2,7‐positions. It was confirmed that macrocycle <jats:bold>1</jats:bold>, bearing bulky substituents at the outer peripheral positions, behaves as a monomeric form in solution without π‐stacking self‐association. Macrocycle <jats:bold>1</jats:bold> has an inner‐cavity size that allows specific inclusion of [9]cycloparaphenylene ([9]CPP), but not [8]CPP or [10]CPP, through an aromatic edge‐to‐face CH‐π interaction.</jats:p>

DOI： 10.1002/ange.202012120

DOI： 10.1002/chem.202203462_references_DOI_SXtoafInqazD6zZ8vYjt6VYRsjT

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ange.202012120

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Photoconversion processes such as electron injection (photooxidation) and dye regeneration (reduction) in dye-sensitized solar cells (DSSCs) occur at considerably inhomogeneous semiconductor/dye/electrolyte interfaces, implying a very high heterogeneity of interfacial photoconversion kinetics. Herein, we present a temporally and spatially resolved investigation of DSSCs comprising a cover glass photoanode with a 100-nm thick TiO2 layer loaded with the metal-free organic dye sensitizer MK-2, which is performed by employing laser scanning microscopy (LSM) for the simultaneous measurement of the photocurrent (PC) and photoluminescence (PL) of DSSCs under short-circuit conditions. Analysis of PL decay curves and the excitation rate dependences of PC and PL obtained for local (or submicrometric) areas of the MK-2-DSSC allows disclosing and quantifying three types of dyes coexisting in the DSSCs: (i) a dye that only generates PC ("PC-dye," 75% of total dye molecules in the DSSC), (ii) a dye that generates both PC and PL ("PCPL-dye," 20%), and (iii) a dye that only generates PL ("PL-dye," 5%). Considering recent theoretical reports on cyanoacrylic dyes, we propose that the PC-dye and the PCPL-dye are covalently bound on a TiO2 surface with different adsorption modes (presumably bidentate and tridentate bridging configurations), whereas the PL-dye is noncovalently trapped within a mesoporous TiO2 film.

DOI： 10.3390/en13081866

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Despite the huge effort that has been devoted to the atomically precise synthesis and structural and physicochemical property characterization of ligand-protected noble metal clusters, quantitative knowledge of thermodynamic equilibrium in solutions of these clusters to date remains lacking. In this article, we report the determination of equilibrium constants for reversible binding-dissociation reactions of a secondary ligand, triphenylphosphine (TPP), in Ag-29(BDT)(12)(TPP)(x) (x = 0-4) clusters (BDT: 1,3-benzenedithiolate) achieved through photoluminescence (PL) analysis. Detailed analyses of TPP-concentration dependencies of PL decay times and PL quantum yields of the clusters under equilibrium allowed us to extract the PL lifetimes (tau(x)) and PL quantum yields (Phi(x)) of each composition (x = 0-4). Using these PL parameters, we reveal in this study how the relative abundances of each composition vary with the TPP concentration. From the simulation of these dependencies, we obtained the stability and equilibrium constants for each binding-dissociation reaction step in the sequential equilibrium. More importantly, the parent clusters, Ag-29(BDT)(12)(TPP)(4), in the solution underwent sequential loss of TPP ligands and became the binding-dissociation equilibria due to modest magnitudes of the equilibrium constant (K = 10(2)-10(4) M-1). Hence, our PL analysis approach is highly effective in determining the photophysical and thermodynamic parameters of inseparable clusters in dynamic equilibrium.

DOI： 10.1021/acs.jpcc.9b11928

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Symmetric multipolar (e.g., quadrupolar and octupolar) chromophores that undergo excited-state symmetry breaking in polar solvents have been drawing considerable attention for a long time as promising two-photon absorption and luminescent materials. However, this process has been generally restricted to liquid media. Herein, we report the excited-state symmetry breaking of a centrosymmetric D-pi-D (donor-pi-donor) quadrupolar molecule, DB2, occurring at a polymer/glass interface. In polar liquids, DB2 exhibits pronounced emission solvatochromism originating from symmetry-breaking intramolecular charge transfer in the S-1 state. Single-molecule fluorescence spectroscopy shows that the fluorescence characteristics of DB2 at the interface are strikingly different from those of DB2 embedded in a polymer film, that is, the dramatic lengthening of fluorescence lifetimes and pronounced sharpening of fluorescence spectra are observed. With the aid of theoretical calculations, it is revealed that these characteristic behaviors are due to the strong electronic localization of the emitting excited state via asymmetric in-plane relaxation of the pi-conjugated framework through dipolar interactions with the glass surface.

DOI： 10.1021/acs.jpcc.9b03612

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Multipolar chromophores (e.g., quadrupolar and octupolar molecules) have excellent two-photon absorption properties and exhibit characteristic excited-state relaxation behaviors that involve structural symmetry breaking. Environmental rigidity could provide an appreciable impact on such conformational rearrangement in the excited state; however, details of its effect remain unclear. Herein, we undertake an ensemble and single-molecule spectroscopic investigation into the effects of environmental rigidity on the photophysical characteristics and behaviors of a newly synthesized D-pi-A-pi-D (donor-pi-acceptor-pi-donor) quadrupolar chromophore, QC, and its pi-A-pi analogue, AC, in various solutions and polymers. The fluorescence emission of QC in nonpolar solvents takes place in the symmetric quadrupolar state [D delta+-pi-A(delta-)-pi-D delta+]*,whereas the significant fluorescence quenching is observed with increasing solvent polarity, suggesting the gradual stabilization of the nonemissive symmetry-broken dipolar state [D delta+-pi-A-(delta-)]*-pi-D or D-pi-[A(delta-)pi-D delta+]* in more polar solvents. However, because of a lack of environmental rearrangement, this dipolar state is not effectively stabilized in a polar polymer matrix. Single-molecule fluorescence spectroscopy was used to explore how environmental rigidity affects the photophysical behaviors of QC and AC. In a rubbery poly(methyl acrylate) (PMA) film, the QC and AC single molecules exhibited fluorescence properties similar to those in nonpolar solutions. Remarkably, the average fluorescence lifetime of QC in the glassy PMA film was longer than that in the rubbery film. Moreover, the heterogeneity of single-molecule fluorescence lifetimes increased considerably, although such variation was not observed for the nonquadrupolar chromophore AC. Experimental and theoretical considerations suggest that fluorescence emission of QC embedded in the rubbery polymer most probably occurs from the symmetric quadrupolar state formed through planarization, whereas such conformational relaxation is suppressed in the glassy polymer because the physical constraint and various degree-of-twist conformations of QC emit fluorescence photons. Overall, this study reveals that environmental rigidity appreciably alters the photophysical characteristics and behaviors of quadrupolar chromophores.

DOI： 10.1021/acs.jpcc.8b03889

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The geometric and electronic properties of silicon-atom-doped aluminum clusters, AlnSim (n = 7-30, m = 0-2), were investigated experimentally. The size dependences of the ionization energy and electron affinity of AlnSim show that the stability of AlnSim is governed by the total number of valence electrons in the clusters, where Al and Si atoms behave as trivalent and tetravalent atoms, respectively. Together with theoretical calculations, it has been revealed that neutral Al10Si and Al12Si have a cage-like geometry with central Si atom encapsulation and closed electronic structures of superatomic orbitals (SAOs), and also that they both exhibit geometric robustness against reductive and oxidative changes as cage-like binary superatoms of Si@Al-10 and Si@Al-12. As well as the single-atom-doped binary superatoms, the effect of symmetry lowering was examined by doping a second Si atom toward the electron SAO closing of 2P SAO, forming Al11Si2. The corresponding anion and cation clusters keep their geometry of the neutral intact, and the ionization energy is low compared to others, showing that Al11Si2 is characterized to be, Si@Al11Si as an alkaline-like binary superatom. For Al21Si2, a face-sharing bi-icosahedral structure was identified to be the most stable as dimeric superatom clusters.

DOI： 10.1039/c7cp03409a

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The fluorescence blinking phenomenon, which is ubiquitous in single nano-objects, provides kinetic information concerning the underlying photophysics in these objects. However, considerable attention should be paid to the blinking analysis of these objects, especially, when they comprise multiple competitive processes. Here we report on a new protocol for discriminating between the competitive photophysical processes that cause fluorescence blinking. A robust statistical analysis was conducted by progressively changing a range of data to reveal the true blinking statistics caused by the electron-transfer dynamics at dye-TiO2 interfaces.

DOI： 10.1246/cl.170127

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We combine results from several different experiments to investigate the photophysics of acridine (Ac) and its hydrated clusters in the gas phase. Our findings are also compared with results from condensed phase studies. Similar to measurements of Ac dissolved in hydrocarbons, the lifetime of the first electronically excited state of isolated Ac in vacuum is too short for typical resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF) experiments, hence no signal from REMPI and LIF can be attributed to monomeric Ac. Instead, sensitized phosphorescence emission spectroscopy is more successful in revealing the electronic states of Ac. Upon clustering with water, on the other hand, the lifetimes of the excited states are substantially increased to the nanosecond scale, and with two water molecules attached to Ac, the lifetime of the hydrated cluster is essentially the same as that of Ac in aqueous solutions. Detailed REMPI and ultraviolet-ultraviolet hole-burning experiments are then performed to reveal the structural information of the hydrated clusters. Although the formation of hydrogen bonds results in energy level reversal and energy separation between the first two excited states of Ac, its effect on the internal geometry of Ac is minimal, and all clusters with 1-3 water molecules demonstrate consistent intramolecular vibrational modes. Theoretical calculations reveal just one stable structure for each cluster under supersonic molecular beam conditions. Furthermore, different from mono-and di-water clusters, tri-water clusters consist of a linear chain of three water molecules attached to Ac. Consequently, the fragmentation pattern in the REMPI spectrum of tri-water clusters seems to be dominated by water trimer elimination, since the REMPI spectrum of Ac+ . W3 is largely reproduced in the Ac+ mass channel, but not in the Ac+ . W1 or Ac+ . W2 channel. Published by AIP Publishing.

DOI： 10.1063/1.4979631

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Supramolecular complexation of gamma-cyclodextrin (gamma-CD) with N,N'-bis(2,6-dimethylphenypperylene-3,4,9,10-tetracarboxylic (DMP-PDI) or N,N'-bis(2,6-dioctyl)perylene-3,4,9,10-tetracarboxylic diimide (C8-PDI) dye in an aqueous solution and in a gamma-CD solid film were investigated via ensemble and single-molecule fluorescence spectroscopy. These two perylene diimide derivatives possess almost the same electronic structure but have different terminal functional groups. This structural difference leads to formation of an inclusion complex of gamma-CD with DMP-PDI but not with C8-PDI in aqueous solution. In a gamma-CD solid film, the distributions of the wavelengths of emission maximum (lambda(em)(max)) are strikingly different between these two dyes; a much narrower and blue-shifted lambda(em)(max) distribution was observed for C8-PDI relative to DMP-PDI. This difference is attributed to the fact that the C8-PDI molecules are bound at the gamma-CD/glass interface as a result of spin-coating of the sample solution, whereas the DMP-PDI molecules form 1:1 and 1:2 inclusion complexes with conformational heterogeneities in the film. In comparison to the case for C8-PDI, more frequent on off blinking events were observed for DMP-PDI. The blinking statistics of DMP-PDI in the gamma-CD film exhibit both single-exponential and nonexponential (i.e., dispersive) kinetics, revealed by robust statistical analysis. Energetic consideration with the aid of theoretical calculations suggests that the underlying photophysics most probably involves hydrogen atom transfer (HAT) between the DMP-PDI guest and gamma-CD host via higher excited (n, pi*) triplet states. The hypothesis of HAT in the inclusion complex reasonably explains the experimental results; however, a charge transfer hypothesis cannot explain the results. The dispersive kinetics is attributable to the effect of thermal fluctuation in the forward and backward HAT reactions.

DOI： 10.1021/acs.jpca.6b11353

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Cyclic arylene ethynylene hexamer 1, composed of alternating 2,7-anthrylene ethynylene units and meta-phenylene ethynylene units, was synthesized. It shows C-3 symmetry and possesses a flat and rigid conformation with a large equilateral triangle-like cavity. Macrocycle 1 self-associates through pi-pi stacking interactions between the anthracene-containing macrocyclic aromatic cores with indefinite-association constant K-E=6980 M-1 in CDCl3 at 303 K. Macrocycle 1 also self-assembles into pi-stacked nanofibers in the drop-cast film.

DOI： 10.1002/chem.201603627

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The effects of supramolecular encapsulation on the photophysics and photostability of a highly fluorescent dimeric derivative of 2,6-diacetox-y-9,10-bis(arylethynyl)anthracene (G2) were investigated by single-molecule fluorescence spectroscopy (SMFS). The fluorescence properties of free-G2 and its self-assembled boronic ester encapsulation complex, G2@(Cap)(2), were compared in solution and a glassy polymer film. The fluorescence spectral characteristics and theoretical calculations suggest that the environment affects the excited-state conformation and subsequent fluorescence emission of G2@(Cap)(2). In particular, in the liquid and polymer environments, G2@(Cap)(2) emits a fluorescence photon in the planar and twist conformation, respectively, whereas the fluorescence-emitting conformation of free-G2 is planar in both environments. The luminous conformation differences between free-G2 and G2@(Cap)(2) in polymer are reflected in the intersystem crossing (ISC) parameters (the ISC quantum yield and triplet lifetime), as determined by fluorescence autocorrelation analysis. The photobleaching yield revealed a 3-fold enhancement in the photostability of encapsulated G2 (relative to free-G2). Under the SMFS measurement conditions, the photostability of the encapsulation complex was independent of the guest's photostability and appeared to be dominated by the thermal stability of the Cap host molecule.

DOI： 10.1021/acs.jpca.6b08734

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Fluorescence on-off blinking of single perylenediimide (DMP-PDI) dyes embedded in a disordered matrix of poly(methyl methacrylate) (PMMA) was investigated by single-molecule fluorescence spectroscopy. In particular, we examined the bin-time dependencies of the complementary cumulative distribution functions (cCDF) of the on-time and off-time durations. It appears that intersystem crossing (ISC) within DMP-PDI competes with charge transfer between DMP-PDI and PMMA. The single-molecule and ensemble cCDFs of the on-time and off time durations (induced by charge transfer) were best described by Weibull functions and log-normal functions, respectively. The dispersive kinetics of the on-time duration were attributed to radical ion pair ISC from triplet charge separation ((CS)-C-3) state to the corresponding singlet ((CS)-C-1) state via charge hopping between charge trap sites in PMMA. This process should compete with triplet charge recombination ((CR)-C-3) which restores the triplet state. On-to-off switching occurs only when (CS)-C-3 -&gt; (CS)-C-1 ISC overcomes the (CR)-C-3 process. The resultant Weibull distribution (with A &lt; 1) reflects that the probability of charge hopping rapidly decreases with time. On the other hand, the off time log-normal kinetics of single-molecules are explained by a Gaussian distribution of activation energies for charge recombination (the so-called Albery model). A simulation study revealed that the ensemble off-time cCDF included power-law kinetics of charge hopping in the polymer matrix.

DOI： 10.1021/acs.jpcc.6b04114

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Newly developed simultaneous scanning photocurrent and luminescence microscopy was applied to ruthenium-based dye-sensitized solar cells (DSCs) comprising a cover glass photoanode with a 100 nm thick TiO2 layer. Using this, we have investigated the lateral variations of several parameters of these DSCs under short-circuit conditions. Simultaneous measurement of photocurrent and luminescence images for the same area of the DSC demonstrated submicrometric lateral resolution of our photo current microscopy, which is approximately 10 times better than the resolution of photo current microscopy used in past studies. The photovoltaic parameters, such as short-circuit current density, open-circuit voltage, and charge-collection efficiency, were thus evaluated for local (or submicrometric) regions of the DSCs. Furthermore, the photocurrent saturation behavior of the DSCs was examined as a function of the excitation rate and analyzed on the basis of a three-state kinetic model. This protocol allowed for quantification of the dye-adsorption number and dye-regeneration rate constant for any local area of the DSCs. Consequently, the correlations between the dye adsorption number, photovoltaic parameters, and regeneration rate constant, which are difficult to address through examination of the entire cell, were revealed by the "zoom-in" approach utilizing this high-resolution photocurrent microscopy.

DOI： 10.1021/acs.langmuir.5b01581

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Organoeuropium sandwich clusters, comprising europium (Eu) and 1,3,5,7-cyclooctatetraene (COT) (Eu-n(COT)(m)), were produced in the gas phase using a laser vaporization synthesis method. Photoionization mass spectra revealed an exclusive Eu-n(COT)(m) formation with three compositions: m = n + 1, m = n, and m = n - 1, which, we propose, correspond to full-sandwich, half-sandwich, and inverted-sandwich structures, respectively. The charge distributions, metal-ligand bonding characteristics, and electronic structures of the clusters were comprehensively investigated by photoionization measurements of Eu-n(COT)(m) neutrals and by photoelectron spectroscopy of Eu-n(COT)(m)(-) and isoelectronic Ba-n(COT)(m)(-) anions. The results confirmed that (1) highly ionic metal-ligand bonding is formed between Eu2+ and COT2- within the sandwich structure (at the termini, ionic forms are Eu+ and COT-) and (2) size dependence of orbital energy can be explained by the Coulombic interaction of simple point charge models between the detaching electrons and dipoles/quadrupoles. When the terminus of the sandwich clusters is Eu2+, COT2-, or Eu, the orbital energy of the electron detachment channel at the opposite terminus strongly depends on the cluster size. In this case, the molecular stack behaves as a one-dimensionally aligned dipole; otherwise, it behaves as a quadrupole, and the relationship between cluster size and electron detachment energy is much weaker. The study also reports on the 4f orbital energy in Eu ions and the formation mechanism of organoeuropium sandwich nanowires up to 12 nm in length. The nanowires are formed by successive charge transfer at the terminal part, Eu+ and COT-, which reduces the ionization energy and increases the electron affinity, respectively.

DOI： 10.1021/jp5011007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The self-assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6-diacetoxy-9,10-bis(arylethynyl)anthracene derivatives 4a-4c as highly fluorescent cruciform guests to form complexes 4a@3, 4b@3, and 4c@(3)(2). The structural features of capsule 3, which possesses two polar bowl-shaped aromatic cavity ends and four large equatorial windows connected by dynamic boronic ester bonds, made it possible to encapsulate cruciform 4 with protection of the reactive anthracene core inside the capsule and with two protruding arylethynyl groups, the -conjugated arms of compound 4, through two of the equatorial windows of the capsule. Thus, complexes 4a@3, 4b@3, and 4c@(3)(2) show greater resistance to photochemical reactions in solution and fluorescence quenching in the powder state compared to free guests 4. In addition to the improved photostability, restriction of the free rotation of the arylethynyl groups of guests 4 upon encapsulation results in sharpening of the UV/Vis absorption peaks with a red-shift and a significant increase in some of the two-photon-absorption peaks of complexes 4a@3, 4b@3, and 4c@(3)(2) compared with free guests 4.

DOI： 10.1002/asia.201400042

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

For single-molecule fluorescence studies, highly photostable fluorophores are absolutely imperative, because photo-induced degradation (i.e., photobleaching) limits the observation time of individual molecules. Herein, the photophysics and photostability of a highly fluorescent 9,10-bis(phenylethynyl) anthracene derivative (G) and its self-assembled boronic ester encapsulation complex (G@Cap) embedded in a glassy polymer matrix are investigated by single-molecule fluorescence spectroscopy (SMFS). The heterogeneity of the fluorescence emission wavelength and triplet blinking kinetics of the guest G are significantly decreased by supramolecular encapsulation due to conformational restriction and reduced heterogeneity in the local environment. A nearly 10-fold increase in the photostability of G due to encapsulation is quantitatively confirmed by evaluating the photobleaching yields of G and G@Cap. In addition, it is found that the G@Cap is &gt; 30-fold more photostable than rhodamine 6G, a widely used fluorescent dye in single-molecule studies. These results demonstrate that the G@Cap can serve as a very bright, long-lasting fluorescent probe for single-molecule studies.

DOI： 10.1039/c4pp00065j

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A series of tetracene (Tc)-doped p-terphenyl (pTP) nanoparticles (Tc/pTP-NPs) were produced at various doping ratios by reprecipitation in water. The Tc/pTP-NPs are disk-like with a mean diameter of 75 nm and height of 7 nm, which were determined by scanning electron microscopy and atomic force microscopy, and exhibited electronic delocalization through H-type aggregation of the pTP molecules. Electronic energy transfer in the Tc/pTP-NPs was examined using steady-state and time-resolved fluorescence spectroscopy and fluorescence anisotropy experiments: pTP-NPs serve as an excellent light-harvesting nano-matrix with a large absorption coefficient that exceeds 10(9) M (1) cm (1). Furthermore, Stern-Volmer analysis of the donor emission was performed by changing the dopant concentration; this showed that a single Tc acceptor quenched more than 10(4) pTP donors. Comparison of the experimental and theoretical energy transfer efficiencies indicated that the efficient energy transfer can be attributed to two-dimensional exciton diffusion in the host nanoparticles. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemphys.2013.01.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The photophysics and photostability of 9,10-bis(phenylethynyl) anthracene (BPEA) diluted in a 40-nm-thick Zeonex polymer film have been investigated by single-molecule spectroscopy (SMS). The single-molecule detection of BPEA was verified by recording fluorescence intensity trajectories, fluorescence lifetimes, and fluorescence spectra. The intensity trajectories showed frequent on/off blinking and one-step photobleaching behaviors. The observed blinking was attributed to the temporary occupation of the excited triplet state T-1 via intersystem crossing (ISC). Assuming a three-state model (e.g., S-0, S-1, and T-1), the distributions of triplet lifetime and S-1 -&gt; T-1 ISC quantum yield of BPEA were both derived from the analyses of the blinking statistics and the intensity autocorrelation. We found extremely low ISC yields (on the order of 10(-5)-10(-4)), which were theoretically rationalized by the large energy gap between B-3(2u) and S-1(B-1(1u))/T-1(B-3(1u)) states. SMS measurements were also conducted under both air and Ar atmospheres in order to gain insight into the influence of oxygen on photobleaching. The results reveal that, although the presence of oxygen considerably degraded the photostability of BPEA, under deoxygenated conditions, BPEA delivers more than 10(7) photons before photobleaching and possesses an appreciably low photobleaching yield of 10(-9)-10(-8). This study shows that BPEA has a relatively high degree of photostability at room temperature and can serve as a useful green fluorescent probe for SMS studies.

DOI： 10.1039/c2ra21100a

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A hexadecyl monolayer covalently attached to Si(111) surfaces (C(16)-Si(111)) was prepared at; 200 degrees C from 1-hexadecene. Formation of the monolayer was characterized by water contact all-le measurement, attenuated total reflection infrared (ATR-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Gas phase synthesized vanadium (V)-benzene (Bz) 1:2 (VBz(2)) sandwich Clusters were size-selectively deposited onto the C(16)-Si(111) substrate thus prepared and an oxidized Si substrate. Investigation of the resultant. clusters, was implemented by thermal desorption spectroscopy (TDS). About 30 K increase ill threshold desorption temperature of the landed clusters was observed oil going from the oxidized Si to the C(16)-Si(111) substrate, a, result indicating that. the clusters are more strongly bound to the C(16)-Si(111) than to the oxidized Si. This result was explained by the penetration of the landed clusters into the hexadecyl monolayer.

DOI： 10.1140/epjd/e2009-00069-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Multiple-decker vanadium-benzene sandwich clusters V(n)(beuzeue)(n+1) produced by a laser-vaporization synthesis method were soft-landed onto self-assembled monolayers of alkanethiol (C(18) H-SAM) and fluorinated alkanethiol (C(10)F-SAM) at 200 K. Noncontact atomic force microscopy has been used to examine the resulting adsorption states Of the Clusters lauded on the SAMs at room temperature. For each SAM substrate, the aggregates of the deposited clusters were observed at the vacancy islands and near the steps of the SAM surface. The result indicates that., at room temperature, the clusters landed Oil the SAM substrate thermally diffuse on the surface to form columnar-shape islands around the defect sites, of the SAM surface.

DOI： 10.1140/epjd/e2009-00068-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Gas-phase synthesized Cr(benzene)(2) sandwich complexes were soft-landed onto a carboxyl-terminated self-assembled monolayer (C15COOH-SAM) on a gold substrate at hyperthermal collision energy (5-20 eV). The deposition process and adsorption properties of the soft-landed complexes were investigated by means of infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) measurements. With the soft-landing, the Cr(benzene)(2) complexes are adsorbed at the SAM surface while keeping their native sandwich structure intact even after the hyperthermal collision event. Moreover, the complexes tend to orient their molecular axes reasonably or comparatively close to the surface normal direction to the SAM surface. This orientation might arise from chemical interactions between the benzene ring in the sandwich complexes and carboxyl groups on the SAM surface. An Arrhenius analysis of the TPD spectra reveals the desorption activation energy of soft-landed complexes as 133 +/- 10 kJ/mol, a value which is comparable to typical adsorption heat of chemisorptions. Chemical interactions between the Cr(benzene)(2) complexes and carboxyl groups would provide firm trapping of the complexes at the SAM surface, preventing the supported complexes from being desorbed until near room temperature.

DOI： 10.1021/jp807137p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Gas-phase-synthesized chromium-benzene 1:2 sandwich cation complexes [Cr+(benzene)(2)] were soft-landed on a self-assembled monolayer (SAM) of fluorinated alkanethiol (C10F-SAM) at a hyperthermal collision energy of similar to 20 eV. The adsorption properties and thermal stability of the soft-landed complexes were studied with infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The landed complexes were neutralized due to charge transfer from the SAM substrate, but their native sandwich structure remained intact. The hyperthermal collision event resulted in the penetration of the incoming complexes into the C10F-SAM matrix. The embedded complexes then tended to orient their molecular axes approximately along the surface normal. This orientational preference is measurably different from that of complexes isolated in alkanethiol SAM matrices, a discrepancy that might be caused by a repulsive interaction between the pi cloud of the capping benzene rings of the complex and the side-chain CF2 groups of the fluorocarbon chains in the C10F-SAM matrix. The thermal desorption study showed that the complexes supported inside the C10F-SAM could resist thermal desorption until the high-temperature region of similar to 320 K, a persistence revealing a large desorption activation energy (similar to 190 kJ/mol).

DOI： 10.1021/jp8055784

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Metal-rich K1-5(KI)(n)(+) (n similar to 27) clusters were produced by the supersonic cooling expansion of laser-induced KI plasma. The obtained mass spectroscopic peaks show the unique magic numbers at n = 9, 13, and 22 for K-1(KI)(n); n = 8, 12, and 21 for K-2(KI)(n); n = 8, 12, 16, and 21 for K-3(KI)(n); n 7, 9, 11, and 13 for K-4(KI)(n); and n = 12 and 21 for K-5(KI)(n). These magic numbers are fairly different from those of other reported metal-rich Na1-9(NaF)(n)(+) and Cs1-5(CsI)(n)(+) clusters. It is interesting to note that K-2.3,K-5(KI)(n)(+) clusters have the same magic numbers at n = 12 and 21 and possess structures that are closely related to the 3 x 3 x 3 and 3 x 3 x 5 cubic structures with the excess electron at the side anion vacancy or the center anion vacancy. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molstruc.2007.02.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Mass spectrometry and photoelectron spectroscopy of o-, m-, and p-terphenyl cluster anions, (o-TP)(n)(-) (n = 2-100), (m-TP)(n)(-) (n = 2-100), and (p-TP)(n)(-) (n = 1-100), respectively, are conducted to investigate the effect of molecular shape on the molecular aggregation form and the resultant ion core character of the clusters. For (o-TP)(n)(-) and (m-TP)(n)(-), neither magic numbers nor discernible isomers are observed throughout the size range. Furthermore, their vertical detachment energies (VDEs) increase up to large n and depend linearly on n(-1/3), implying that they possess a three-dimensional (3D), highly reorganized structure encompassing a monomeric anion core. For (p-TP)(n)(-), in contrast, prominent magic numbers of n = 5, 7, 10, 12, and 14 are observed, and the VDEs show pronounced irregular shifts below n = 10, while they remain constant above n = 14 (isomer A). These results can be rationalized with two-dimensional (2D) orderings of p-TP molecules and different types of 2D shell closure at n = 7 and 14, the monomeric and multimeric anion core, respectively. Above n = 16, the new feature (isomer B) starts to appear at the higher binding side of isomer A, and it becomes dominant with n, while isomer A gradually disappears for larger sizes. In contrast to isomer A, the VDEs of isomer B continuously increase with the cluster size. This characteristic size evolution suggests that the transition to modified 2D aggregation forms from 2D ones occurs at around n = 20.

DOI： 10.1021/jp801159n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Gas-phase synthesized transition metal-benzene sandwich complexes of M(benzene)2 (M = Ti, V, and Cr) are soft-landed onto a self-assembled monolayer of n-octadecanethiol (C-18-SAM) at a collision energy of 10-20 eV. The resulting adsorption states and thermal desorption kinetics of the soft-landed complexes are studied with infrared reflection absorption spectroscopy and temperature-programmed desorption. The complexes keep their native sandwich structure intact on the SAM substrate even after the "hyperthermal" deposition event. The soft-landed complexes are oriented with their molecular axes largely tilted off the surface normal of the SAM substrate and exhibit unusually large desorption activation energies (E-d = similar to 130 kJ/mol). For comparison, thermal deposition (similar to 25 meV) of Cr(benzene)2 vapor onto the C-18-SAM, carried out using a physical vapor deposition technique, showed that the complexes are weakly physisorbed (E-d = similar to 70 kJ/mol) on the SAM with a random orientation. Only a hyperthermal collision event allows the incident complexes to penetrate into the SAM matrix. The desorption of the embedded complexes in the SAM is then suppressed to around room temperature and may be associated with the crystal-rotator phase transitions of the SAM matrix.

DOI： 10.1021/jp711695s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The electronic structures and structural morphologies of naphthalene cluster anions, (naphthalene)(n)(-) (n=3-150), and its related aromatic cluster anions, (acenaphthene)(n)(-) (n=4-100) and (azulene)(n)(-) (n=1-100), are studied using anion photoelectron spectroscopy. For (naphthalene)(n)(-) clusters, two isomers coexist over a wide size range: isomers I and II-1 (28 &lt;= n &lt;= 60) or isomers I and II-2 (n &gt;= similar to 60). Their contributions to the photoelectron spectra can be separated using an anion beam hole-burning technique. In contrast, such an isomer coexistence is not observed for (acenaphthene)(n)(-) and (azulene)(n)(-) clusters, where isomer I is exclusively formed throughout the whole size range. The vertical detachment energies (VDEs) of isomer I (7 &lt;= n &lt;= 100) in all the anionic clusters depend linearly on n(-1/3) and their size-dependent energetics are quite similar to one another. On the other hand, the VDEs of isomers II-1 and II-2 produced in (naphthalene)(n)(-) clusters with n &gt;= similar to 30 remain constant at 0.84 and 0.99 eV, respectively, 0.4-0.6 eV lower than those of isomer I. Based upon the ion source condition dependence and the hole-burning photoelectron spectra experiments for each isomer, the energetics and characteristics of isomers I, II-1, and II-2 are discussed: isomer I is an internalized anion state accompanied by a large change in its cluster geometry after electron attachment, while isomers II-1 and II-2 are crystal-like states with little structural relaxation. The nonappearance of isomers II-1 and II-2 for (acenaphthene)(n)(-) and (azulene)(n)(-) and a comparison with other aromatic cluster anions indicate that a highly anisotropic and symmetric pi-conjugated molecular framework, such as found in the linear oligoacenes, is an essential factor for the formation of the crystal-like ordered forms (isomers II-1 and II-2). On the other hand, lowering the molecular symmetry makes their production unfavorable. (c) 2008 American Institute of Physics.

DOI： 10.1063/1.2903473

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The evolution of the electronic structure of molecular aggregates is investigated using anion photoelectron (PE) spectroscopy for anionic clusters of anthracene (Ac) and its alkyl derivatives: 1-methylanthracene (1MA), 2-methylanthracene (2MA), 9-methylanthracene (9MA), 9,10-dimethylanthracene (DMA), and 2-tert-butylanthracene (2TBA). For their monomer anions (n=1), electron affinities are confined to the range from 0.47 to 0.59 eV and are well reproduced by density functional theory calculations, showing the isoelectronic character of these molecules. For cluster anions (n=2-100) of Ac and 2MA, two types of isomers I and II coexist over a wide size range: isomers I and II-1 (4 &lt;= n &lt; 30) or isomers I and II-2 (n &gt;=similar to 40 for Ac and n &gt;=similar to 55 for 2MA). However, for the other alkyl-substituted Ac cluster anions (i.e., 1MA, 9MA, DMA, and 2TBA), only isomer I is exclusively formed, and neither isomer II-1 nor II-2 is observed. The vertical detachment energies (VDEs) of isomer I in all the anionic clusters depend almost linearly on n(-1/3). In contrast, the VDEs of isomers II-1 (n &gt;= 14) and II-2 (n=40-100), appeared only in Ac and 2MA cluster anions, remain constant with n and are similar to 0.5 eV lower than those of isomer I. The PE spectra revealed the characteristics of each isomer: isomer I possesses a monomeric anion core that is gradually embedded into the interior of the cluster with increasing n. On the other hand, isomers II-1 and II-2 possess a multimeric (perhaps tetrameric) anion core, but they differ in the number of layers from which they are made up; monolayer (isomer II-1) and multilayers (isomer II-2) of a two-dimensionally ordered, finite herringbone-type structure, in which electron attachment produces only little geometrical rearrangement. Moreover, the agreement of the constant VDEs of isomer II-2 with the bulk data demonstrates the largely localized nature of the electronic polarization around the excess charge in a crystal-like environment, where about 50 molecules provide a charge stabilization energy comparable to the bulk.

DOI： 10.1063/1.2805185

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Photoelectron spectroscopy of tetracene cluster anions, (tetracene), (n = 1 - 100), reveals the coexistence of two types of isomers, designated as isomers I and II-1 (n = 10-50) or isomers I and II-2 (n &gt; 60), in a wide size range. The vertical detachment energies (VDEs) of isomer I increase persistently due to polarization and structural relaxation effects, where a monomeric anion core is encompassed with geometrically reorganized neutral molecules. Conversely, a characteristic ion distribution in the mass spectrum of (tetracene),, ensues from the two-dimensional (2D) herringbone-type ordering of isomer II-1, whose VDEs remain constant at 1.80 eV for n &gt;= 14. Also, isomer II-2, presumably adopting multilayered structural motifs, exhibits invariable VDEs of 2.0 eV, a manifestation of significant charge screening effects in these isomers. The invariable nature of the VDEs of isomers II-1 and II-2 unambiguously demonstrates a largely localized nature of polarization induced by the excess charge residing in microscopic crystal-like environments. Surprisingly, only 14 tetracene molecules within a 2D herringbone-type layer including an excess charge can provide the charge stabilization energy corresponding to similar to 80% of that of the crystal, and the rest of the energy is provided by polarization of neutral molecules in adjacent layers.

DOI： 10.1021/jp076134h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Uniform-sized silver nanoparticles with average diameter of 13.7 nm have been prepared in the gas-phase by combining a pulsed laser ablation method with a low pressure-differential mobility analyzer (LP-DMA). By depositing the silver nanoparticles onto a silicon substrate, a granular film consisting of size-selected silver nanoparticles has been fabricated and its morphology and electronic properties have been examined using transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. This granular silver film serves as a highly active substrate for surface-enhanced Raman scattering (SERS).

DOI： 10.1140/epjd/e2007-00064-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The present account describes our efforts to understand the microscopic aspects of condense phase phenomena, such as ion solvation in molecular liquids and charge carrier localization in molecular solids, by viewing finite-size molecular clusters as their embryonic forms. In this effort, we efficiently prepared supersonically cooled, isolated molecular cluster anions with up to more than 100 constituent molecules and size-selectively investigated their electronic structures using anion photoelectron spectroscopy. Large anionic clusters of two different types of organic molecule; acetonitrile and naphthalene reported as examples of the noteworthy results obtained in our studies. In these two systems, we found that energetically close anionic isomers coexist over a broad range in size, and their contribution in the photoelectron spectra could be separated using anion beam hole-burning technique. A detailed inspection into the electronic states and size-dependent energetics of each isomer has enabled us to establish a link from the large finite cluster to the infinite bulk system.

DOI： 10.1246/bcsj.80.1058

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Gas-phase synthesized multidecker V-2(benzene)(3) sandwich complexes were soft-landed onto a self-assembled monolayer of an n-octadecanethiol (C-18-SAM). The infrared absorption spectrum of this complex supported on the C-18-SAM was obtained by infrared reflection absorption spectroscopy (IRAS). The vibrational assignment of the IRAS spectrum for the V-2(benzene)(3) sandwich was based on a harmonic frequency analysis that employed density functional theory. The close similarity between the experimental and calculated results for the IR absorption frequencies demonstrates that the V-2(benzene)(3) complexes have a multidecker sandwich structure on the SAM substrate. Moreover, our thermal desorption study established that the sandwich complexes can be isolated on the SAM substrate up to a high temperature of similar to 350 K.

DOI： 10.1021/ja068442j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Electronic properties of silicon and germanium atom doped indium clusters, InnSim and InnGem, were investigated by photoionization spectroscopy of the neutrals and photoelectron spectroscopy of the anions. Size dependence of ionization energy and electron affinity for InnSi1 and InnGe1 exhibit pronounced even-odd alternation at cluster sizes of n = 10-16, as compared to those for pure In-n clusters. This result shows that symmetry lowering with the doped atom of Si or Ge results in undegeneration of electronic states in the 1d shell formed by monovalent In atoms.

DOI： 10.1021/jp065921w

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Silicon clusters mixed with a transition metal atom, MSin, were generated by a double-laser vaporization method, and the electronic and geometric stabilities for the resulting clusters with transition metal encapsulated by silicon were examined experimentally. By means of a systematic doping with transition metal atoms of groups 3, 4, and 5 (M = Sc, Y, Lu, Ti, Zr, Hf, V, Nb, and Ta), followed by changes of charge states, we explored the use of an electronic closing of a silicon caged cluster and variations in its cavity size to facilitate metal-atom encapsulation. Results obtained by mass spectrometry, anion photoelectron spectroscopy, and adsorption reactivity toward H2O show that the neutral cluster doped with a group 4 atom features an electronic and a geometric closing at n = 16. The MSi16 cluster with a group 4 atom undergoes an electronic change in (i) the number of valence electrons when the metal atom is substituted by the neighboring metals with a group 3 or 5 atom and in (ii) atomic radii with the substitution of the same group elements of Zr and Hf. The reactivity of a halogen atom with the MSi16 clusters reveals that VSi16F forms a superatom complex with ionic bonding.

DOI： 10.1021/jp066757f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Silicon clusters mixed with a transition metal atom, MSin, were generated by a double-laser vaporization method, and the electronic and geometric stabilities for the resulting clusters with transition metal encapsulated by silicon were examined experimentally. By means of a systematic doping with transition metal atoms of groups 3, 4, and 5 (M = Sc, Y, Lu, Ti, Zr, Hf, V, Nb, and Ta), followed by changes of charge states, we explored the use of an electronic closing of a silicon caged cluster and variations in its cavity size to facilitate metal-atom encapsulation. Results obtained by mass spectrometry, anion photoelectron spectroscopy, and adsorption reactivity toward H2O show that the neutral cluster doped with a group 4 atom features an electronic and a geometric closing at n = 16. The MSi16 cluster with a group 4 atom undergoes an electronic change in (i) the number of valence electrons when the metal atom is substituted by the neighboring metals with a group 3 or 5 atom and in (ii) atomic radii with the substitution of the same group elements of Zr and Hf. The reactivity of a halogen atom with the MSi16 clusters reveals that VSi16F forms a superatom complex with ionic bonding.

DOI： 10.1021/jp066757f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The geometric and electronic structures of aluminum binary clusters, AlnX (X) Si and P), have been investigated, using mass spectrometry, anion photoelectron spectroscopy, photoionization spectroscopy, and theoretical calculations. Both experimental and theoretical results show that Al12Si has a high ionization energy and low electron affinity and Al12P has a low ionization energy, both with the icosahedral structure having a central Si or P atom, revealing that Al12Si and Al12P exhibit rare- gas- like and alkali superatoms, respectively. Experiments confirmed the possibility that the change in the total number of valence electrons on substitution could produce ionically bound binary superatom complexes, the binary cluster salts Al12P+F- and Al12B-Cs+.

DOI： 10.1021/jp065161p

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The adsorption state and thermal stability of V( benzene)(2) sandwich clusters soft-landed onto a self- assembled monolayer of different chain-length n-alkanethiols (C-n-SAM, n) 8, 12, 16, 18, and 22) were studied by means of infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The IRAS measurement confirmed that V(benzene)(2) clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80 off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain length of the SAMs. For the longest chain C-22-SAM, the activation energy reaches similar to 150kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature. The clear chain-length-dependent thermal stability of the supported clusters observed here can be explained well in terms of the cluster penetration into the SAM matrixes.

DOI： 10.1021/jp061806+

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Adiabatic electron affinities (EA(a)'S) of seven oligophenyls: biphenyl (BP), 4-cyanobiphenyl (CNBP), o-terphenyl (o-TP), m-terphenyl (m-TP), p-terphenyl (p-TP), p-quaterphenyl (p-QP), and 1,3,5-triphenylbenzene (TPB), have been evaluated by anion photoelectron spectroscopy and density functional theory calculations. The result provides the direct determination of the EA(a) values of the isolated CNBP, p-TP, p-QP, and TPB molecules, while EA(a) of BP, o-TP, and m-TP were estimated from the extrapolation of EA(a) vs cluster size. The excellent agreement between the experimental and calculated EA(a) were obtained.

DOI： 10.1246/cl.2006.888

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effect of Cs atom doping on metallic aluminum clusters and covalent silicon clusters, AlnCsm (n = 5-14, m = 0-3) and SinCsm (n = 5-16, m = 0-3), was examined by mass spectrometry and anion photoelectron spectroscopy. For clusters containing Cs atom(s), the electron affinities of both clusters are generally decreased and the following characteristic features are observed: for AlnCsm Cs-atom doping causes (1) electron filling into the electronic shell structure of the Al-n, clusters and (2) geometrical packing of icosahedral 13-atoms, while for SinCsm Cs-atom doping enhances electronic stability to be ascribed to pure Si-n clusters, particularly at (n, m) = (10, 3) and (13, 1). (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.01.118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The electronic structures of binary gold cluster anions: AunM- (M = Pd, Ni, Zn, Cu, Mg) were investigated by anion photoelectron spectroscopy at the photon energy of 4.66 eV. The spectra exhibit even-odd alternation of electron affinities and characteristic spectral changes with n, which are accountable in terms of the interactions between the Au clusters and doped metal atoms. For the binary clusters containing Pd, Ni, and Cu. their valence electrons are shared with those of the Au clusters, whereas for Mg the doped atom is weakly bound to Au clusters. A size-dependent spectral change is clearly observed for AunPd- at n approximate to 5. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2006.02.034

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Gas-phase synthesized vanadium-benzene 1:2 (VBz(2)) sandwich clusters were size-selectively deposited onto bare gold and long-chain n-alkanethiolate [-S-(CH2)(n-1)-CH3; n = 16, 18, and 22] self-assembled monolayer (SAM)-coated gold substrates under ultrahigh vacuum (UHV) conditions. Investigation of the resulting deposited clusters was performed by infrared reflection absorption spectroscopy (IRAS) and thermal desorption spectroscopy (TDS). The IR frequencies of the soft-landed VBz(2) clusters show excellent agreement with the fundamentals reported in IR data of VBz(2) in an argon matrix. The analysis of IRAS spectra reveals that while there was no orientational preference of the VBz(2) clusters on a bare gold substrate, the VBz(2) clusters deposited onto the SAM substrates were highly oriented with the molecular axis 70-80 degrees tilted off the surface normal. In addition, analysis of TDS spectra revealed unusually large adsorption heats of the physisorbed VBz(2) clusters. The present results are explained by cluster penetration into the long-chain alkanethiolate SAM and for the first time demonstrate the matrix isolation of gas-phase organometallic clusters around room temperature.

DOI： 10.1021/jp057194v

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Evolution of electronic structures of nanoscale biphenyl cluster anions, (BP)(n)(-) (n = 2-100), have been studied by photoelectron spectroscopy in a size-selective fashion. The energetics of vertical detachment energy (VDE) revealed negative electron affinity of a biphenyl molecule and substantial cluster reorganizations via electron attachment. Comparison of the VDE energetics with naphthalene cluster anions implied that the freezing (and/or melting) temperatures of the BP clusters may be much lower than those of naphthalene clusters.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

V(benzene)(2) sandwich cluster cations produced in the gas phase were size-selectively deposited onto a self-assembled monolayer of n-hexadecanethiols (HDT-SAM) chemisorbed on a Au(111) surface as well as onto a bare Au(111) surface. The thermal chemistry of the neutralized clusters on each substrate was studied with temperature programmed desorption (TPD). From the analyses of the threshold in the TPD, the desorption activation energies of the clusters deposited were determined to be 64.4 +/- 12.8 kJ/mol for the Au(111) and 130 +/- 10 kJ/mol for the HDT-SAM. The remarkably large desorption activation energy from the SAM suggests that the deposited clusters are incorporated into the SAM matrix and firmly trapped inside the alkyl chains of the SAM.

DOI： 10.1140/epjd/e2005-00151-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Cluster anions of 2,2'- bithiophene, (2T)(n)(-), were produced up to n similar to 500 in the gas-phase. The energetics of the excess electron in the (2T)(n)(-) clusters with n = 1- 100 were explored by negative ion photoelectron spectroscopy. When the vertical detachment energies (VDEs) obtained from the photoelectron spectra were analyzed by a plot against n(-1/3), it has been revealed that the excess electron trapping level thus extrapolated is located at similar to 0.8 eV below the conduction band minimum (i.e. LUMO) of the 2T thin film. The large slope of the VDEs vs. n(-1/3) plot suggests that the neutral 2T molecules surrounding the anion core take non-planar twisted conformations with permanent dipole moments, resulting in the exceedingly deep trapping of the excess electron in the 2T cluster anions.

DOI： 10.1140/epjd/e2005-00139-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/ja045380t

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Authorship：Lead author  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A molecular beam of europium-cyclooctatetraene sandwich nanowires Eu-n(COT)(m) was produced by a laser vaporization synthesis method. The formation mechanism of the nanowires was quantitatively revealed by photoelectron and photoionization spectroscopies of the Eu-COT species, together with supporting theoretical calculations. From these results. it is confirmed that growth processes extending the length of Eu-COT nanowires involve a series of elementary reactions in which efficient charge transfer occur at the terminal reaction sites. In every elementary step, the reaction proceeds between one reactant having low ionization energy and the other reactant having high electron affinity, probably via a "harpoon" mechanism.

DOI： 10.1021/jp0452103

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Negative ion photoelectron spectroscopy was employed to investigate the electronic structure of the acridine molecular anion and its monohydrated anion in the gas phase. Their adiabatic electron affinities were measured to be 0.896+/-0.010 and 1.18+/-0.05 eV, and the low-lying electronic excited states in both neutral acridine and in its monohydrate were revealed. The photoelectron spectra clearly exhibit the presence of low-lying singlet and triplet states having a (pi,pi*) configuration in an uncomplexed acridine molecule. Comparison of the photoelectron spectrum of acridine with that of anthracene shows that photodetachment processes into the excited states of (n,pi(*)) configuration have little intensity, implying a relatively large intramolecular structural relaxation in the (n,pi(*)) states. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1818132

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Two types of anion states are shown to coexist in nanometer-scale polyacene cluster anions. Naphthalene and anthracene nanoclusters having a single excess electron were produced in the gas-phase. Photoelectron spectra of size-selected cluster anions containing 2 to 100 molecules revealed that rigid "crystal-like" cluster anions emerge, greater than similar to2 nanometers in size, and coexist with the "disordered" cluster anion in which the surrounding neutral molecules are reorganizing around the charge core. These two anion states appear to be correlated to negative polaronic states formed in the corresponding crystals. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1809118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We have studied the electronic structures of several gas phase exohedral lanthanide (Ln)-C-60 clusters, Ln(n)C(60) (Ln=Pr, Ho, Tb, Tm, Eu, and Yb) with n=1-4, by photoionization spectroscopy of the neutrals and photoelectron spectroscopy of their anions. Both of the spectroscopic analyses reveal that most of the Ln atoms preferably take +3 oxidation states, while Eu atoms alone assume +2 oxidation states, and that C-60 accepts up to twelve donated electrons in Ln(n)C(60). An additional photoionization examination of the oxygen atom mixing into the Ln(n)C(60) clusters demonstrated that each oxygen atom reduces two electrons from C-60. This result implies that the number of accepted electrons in C-60 can be varied by a suitable choice of the number of Ln atoms and O atoms. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1767514

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Pyrene molecular anion and its homogeneous clusters, (pyrene)(n)(-) (n = 2-20), have been studied by anion photoelectron spectroscopy. The adiabatic electron affinity (EA(a)) of pyrene was directly determined to be 0.406 +/- 0.010 eV. This EA(a) value agrees with that calculated using the method of density functional theory, showing that the excess electron occupies the lowest unoccupied molecular orbital of pyrene molecule. Photoelectron spectra of its cluster anions suggest that the excess electron in the pyrene dimer anion is delocalized over the two pyrene moieties, whereas in larger clusters the excess electron is predominantly localized on a single pyrene molecule. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2004.03.100

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Net absorptive (Abs) chemically induced dynamic electron polarization (CIDEP) is observed in the system of the lowest excited singlet molecular oxygen O-2((1)Delta(g)) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical in benzene by means of the time-resolved ESR (TR-ESR) spectroscopy. As a result of (1) the analysis of CIDEP time profiles by the modified Bloch and kinetic equations and (2) the quenching of CIDEP by triethylamine, it is confirmed that the Abs CIDEP is created through the interaction of O-2((1)Delta(g)) with TEMPO. The creation of Abs CIDEP is reasonably interpreted in terms of the radical-triplet pair mechanism (RTPM) of the O-2((3)Sigma(g)(-))-TEMPO pair with doublet precursor. The absolute magnitude of net Abs CIDEP created on TEMPO is experimentally estimated to be 340 +/- 40 in the unit of Boltzmann polarization. To our knowledge, this is one of the largest magnitudes of CIDEP measured so far by the TR-ESR method. Based upon the RTPM theory, the origin of this unusually large CIDEP is attributed to the large spin relaxation effect via the electron spin dipole-dipole interaction of O-2((3)Sigma(g)(-)) formed in the quenching process of O-2((1)Delta(g)) by TEMPO. As a result of the discussion about the large CIDEP in O-2((1)Delta(g)) quenching by TEMPO, it is proposed that the quenching takes place through the enhanced intersystem crossing accompanied with strong electron exchange interaction between an oxygen molecule and a TEMPO radical.

DOI： 10.1021/jp035235m

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Authorship：Lead author   Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

Anion photoelectron spectroscopy of acetonitrile cluster anions, (CH3CN)(n)(-) (n=10-100), successfully demonstrates the competitive coexistence of two different anionic species: a solvated electron and a solvent-bound valence anion. The distinctly different nature of these anions is revealed by hole-burning-type photoelectron spectroscopy and relative photodetachment cross section measurements. This unusual coexistence is attributed to the closely lying nature of their anionic states at just the number of solvent molecules sufficient to almost complete the first solvation layer.

DOI： 10.1103/PhysRevLett.91.153002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We present a negative ion photoelectron spectroscopic study on the solvation energetics of an excess electron in the size-selected aromatic hydrocarbon nanoclusters, (benzene)(n)(-) (n=53-124) and (toluene)(n)(-) (n=33-139). The formation and stability of these negatively charged clusters were investigated using mass spectrometry with two different sources: (1) low-energy (approximate to0.3 eV) electron attachment and (2) high-energy electron impact. The results reveal that very large coordination numbers (nsimilar to25) are necessary for the formation of stable benzene and toluene cluster anions. This suggests that the second solvation layer (effect) is essential for stable binding of the excess electron in these clusters. The energetics of the cluster anions were also explored by negative ion photoelectron spectroscopy. The photoelectron spectra obtained were related to bulk parameters, e.g., solvent reorganization energy and conduction band minimum, via an analysis of vertical detachment energies versus n(-1/3). The bulk solvent reorganization energies thus estimated have revealed the excess electron trapping levels in bulk benzene and toluene. The applicability of the generalized cluster size equation is examined in these nondipolar aromatic hydrocarbon systems for the first time. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1516793

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Palladium-doped gold clusters. AunPd- (n = 1-4). were investigated using anion photoelectron spectroscopy at 4.66 eV photon energy. Electron affinities (EAs) and vertical detachment energies (VDEs) are determined, and the electronic structures of Pd-doped Au-n clusters are compared to those of pure Au-n clusters. A peak shape analysis reveals electronic and geometric similarity between Au-n(-) and Aun-1 Pd- clusters and it is found that (1) an electron promotion occurs from 4d to 5s orbital in the Pd atom, and that (2) the bond of Au-Pd is formed through sigma orbital between 6s of Au and 5s of Pd. (C) 2002 Published by Elsevier Science B.V.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Negatively charged benzene clusters, (benzene)(n)(-), were produced by injecting low- and high-energy electrons into an intense supersonic jet expansion. Threshold size of n=53 was observed by slow-electron attachment, while the smaller (benzene)(n)(-) with 2 less than or equal ton less than or equal to 52 were also observed through the fragmentation of larger (benzene)(n)(-) by high-energy electron attachment. Photoelectron spectroscopy for (benzene)(n)(-) with n=53-124 has revealed a bulklike electron solvated state in (benzene)(n greater than or equal to 53)(-) through the vertical detachment energies (VDEs) versus n(-1/3) relationship. (C) 2001 American Institute of Physics.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Time-resolved ESR (TR-ESR) spectra were measured in the laser excitation of aromatic compounds such as xanthone, bromopyrene, fluoranthene (Flt) and pyrene (Py) in sodium dodecyl sulfate (SDS) aqueous micellar system in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). Net emission (Em) signals of triplet hyperfine (hf) lines of TEMPO were observed in xanthone- and bromopyrene-TEMPO systems. The chemically induced dynamic electron polarization (CIDEP) was explained by radical-triplet pair mechanism. Antiphase signals of TEMPO with Ern in low-field side and enhanced absorption in high-field side (EA) of each triplet hf line were superimposed on net Ern signals in Flt- and Py-TEMPO systems. The square laser power dependence of the EA signal suggests that the two-photon ionization of Flt and Py is related to the EA antiphase signal. Rate constants of the reactions occurring in SDS solution were determined by analysis of transient absorption decays in the Py-TEMPO system. The reaction rates of Py+-TEMPO and Py-3*-TEMPO in SDS solution were determined as 1.2 X 10(6) s(-1) and 3.0 X 10(5) s(-1), respectively, at the TEMPO concentration of 2 mM (M = mol dm(-3)). According to these measurements, it was concluded that the EA CIDEP is due to spin-correlated radical pair (SCRP) of TEMPO and Py+ which was formed in the electron transfer reaction from TEMPO to Py+. Simulation of TR-ESR spectra was carried out using SCRP theory. From kinetic analysis of intermediates together with the simulation of TR-ESR spectra, it was concluded that both SCRP of Py+-TEMPO and RTPM of Py-3*-TEMPO contribute to the CIDEP of TEMPO.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

As the final part of the series, nonradiative dynamics and energy-level structure of relevant electronic excited states in 9(10H)-acridone (AD) and its hydrated clusters have been studied by various spectroscopic methods. Time-resolved fluorescence measurements on their (1)(pi,pi*) origin excitation have revealed that the fluorescence decay is very fast (approximate to 10 ps) for bare AD but drastically lengthened (&gt; ns) in AD-(H2O)(n) (n = 1-6 and higher). Bare AD has been observed clearly by mass-selective delayed ionization and sensitized-phosphorescence detection, which indicates the efficient formation of molecules in triplet manifold after the (1)(pi,pi*) excitation. Several weak peaks have been identified around each (1)(pi,pi*) vibronic band of bare AD, and they are attributed to (3)(n,pi*) transitions which borrow intensity from the nearby (1)(pi,pi*) bands through the direct spin-orbit coupling. Such satellite bands completely disappear in the fluorescent cluster spectra with n greater than or equal to 1. All of the experimental observations indicate that the dominant nonradiative pathway in bare AD is the S-1(pi,pi*) --&gt; T-2(n,pi*) intersystem crossing (ISC) followed by the T-2(n,pi*) --&gt; T-1(pi,pi*) internal conversion. This direct ISC process becomes prohibited by the energy-level inversion between the S-1 and T2 states induced by the H bonding to the C=O site. Thus the relaxation pathway is "switched" to the second-order ISC [S-1-(pi,pi*) --&gt; T-1(pi,pi*)] in the fluorescent hydrated clusters, where the carbonyl site is involved in H-bonding networks. Owing to the increasing S-1-T-2 separation, the fluorescence quantum yield becomes larger for the higher clusters, which is approaching to the bulk solution value, i.e., Phi(f) approximate to 1. The (pi,pi*) and (n,pi*) shifts at each cluster geometry have been calculated as (N)HOMO-LUMO gaps in DFT orbital energies to support the picture on the energy-level structure. Most importantly, a small falloff in the fluorescence decay constants from n = 2 to 3 has been definitely correlated to the crossover in H-bonding topologies (the C=O bonded --&gt; the bridged form), which has already been established in papers I and TI. The delayed ionization has identified new spectral features that are completely absent in the fluorescence excitation spectrum. They are assigned to the N-H bonded isomer(s) with n less than or equal to 3, which is at least as stable as the C=O bonded conformer(s) with the same size. The ISC in the hydrate(s) should be as fast as in bare AD, because of the lack of the S-1-T-2 level inversion. These experimental findings demonstrate the site-specific solvation effects on the electronic energy-level structure and the resultant nonradiative dynamics in the hydrated clusters of a bifunctional molecule.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The present paper represents fluorescence-detected infrared measurements of 9(10H)-acridone (AD) and 10 of its fluorescent hydrated clusters, AD-(H2O), (n = 1-5 and more), which have been performed by monitoring the fluorescence from their (1)(pi,pi*) electronic origin transitions reported in paper I. In the n = 1 and 2 clusters, free N-H stretching band has been identified in addition to O-H stretching bands characteristic to water molecules acting as single proton donors. As the next solvation step, the II-bonded O-H stretches are further developed in the red-shifted region and the N-H stretch becomes involved in the hydrogen-bonds for the n = 3-5 clusters. For n greater than or equal to 6, more than one pair of double-donor O-H stretches appear. These spectral features are well correlated to the stepwise evolution in the hydrogen-bonding networks in AD-(H2O)(n), which have been predicted by the (pi,pi*) spectral-shift analysis and DFT calculations presented in paper I: water units are bound to the C=O site for n = I and 2, a single water chain bridges between the C=O and N-H sites above the AD aromatic rings for n = 3-5, and water bridges become branched for n greater than or equal to 6 and probably form three-dimensional cages at higher aggregation levels. Differences in hydrogen-bonding topologies, stabilities, and dynamical behaviors among the conformers are discussed on the basis of the experimental observations, the DFT calculations, and comparison with other hydrated aromatic clusters.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A series of papers (I-III) reports spectroscopic investigation on structure and dynamics of 9(10H)-acridone (AD) and its hydrated clusters. As the first part of the series, the present paper describes their lowest (1)(pi,pi*) electronic transition in the 370-400 nm region studied by fluorescence-based laser spectroscopy and mass-selective two-color resonance-enhanced two-photon ionization (2C-R2PI). Thirteen fluorescent hydrates as well as the monomer have been identified in fluorescence-excitation and UV-UV hole-burning measurements, and size assignments for relatively smaller clusters, AD-(H2O), (n = 1-6), have been conducted by 2C-R2PI. The origin bands for larger-size clusters show larger red shifts converging at ca. 2200 cm(-1) but the changes are nonmonotonic, with a substantial increase from n = 2 to 3. Density-functional-theory (DFT) calculations at the B3LYP/6-31G(d,p) level have predicted that the energy difference between the C=O and N-H bonded isomers is quite small (only approximate to 1 kcal/mol) for n = 1 and 2. The observed spectral shifts of fluorescent hydrates with n = 1 and 2 are well reproduced by the HOMO-LUMO gap in the DFT orbital energies of either of the N-H or C=O bonded isomers, leaving the definitive structural assignments to fluorescence-detected infrared spectroscopy which will be described in paper II. For the larger clusters (n 3-5), several minimum-energy structures have been identified within 2 kcal/mol in binding energy, among which the conformers with water molecules bridging between the C=O and N-H sites over the AD's aromatic rings are identified as the observed species, based on good agreement between the calculated and observed spectral shifts.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chemically induced dynamic electron polarization (CIDEP) generated through the interaction between the lowest excited singlet oxygen molecule and 2,2,6,6,-tetramethylpiperidinyl-1-oxyl (TEMPO) radical was observed by the time-resolved ESR technique. Excited singlet oxygen molecules were produced by the triplet sensitizer through energy transfer. Absorptive electron spin polarization was generated on the free radical in the excited singlet oxygen molecule - free radical system, in which the CIDEP generation was interpreted by the radical-triplet pair mechanism with doublet precursor (DP-RTPM). The CIDEP time profile was successfully analyzed by using the Bloch equations. Quenching of O-1(2) by beta-carotene provides further evidence for DP-RTPM in the O-1(2)-TEMPO system.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chemically induced dynamic electron polarization (CIDEP) generated through the interaction of the excited tripler state of benzophenone with the 2,2,6,6,-tetramethyl-1-piperidinyloxyl (TEMPO) radical was investigated by time-resolved ESR spectroscopy in benzene solution. We carefully examined what factors control the CIDEP intensities. By comparing the CIDEP intensity of TEMPO obtained in the triplet benzophenone-TEMPO system with the intensity in the C-60-TEMPO system, the absolute magnitude of net emissive polarization was determined to be -6.9 in the unit of Boltzmann polarization. The emissive polarization is attributed to state mixing between a quarter and a doublet in the radical-tripler pair induced by the zero-field splitting interaction of the counter triplet molecule. Our result is quantitatively explained by the theory that the net CIDEP is generated predominantly in regions where the quarter and doubler levels cross. This indicates that the quenching of the excited triplet benzophenone by TEMPO in benzene can proceed via an electron-exchange interaction.

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：Imperial College Press  

Gas-phase synthesized vanadium-mesitylene 1:2 V(mes)2 cluster cations were size-selectively deposited onto a long-chain alkanethiolate selfassembled monolayer-coated gold substrate under ultrahigh vacuum conditions. Examination of the resultant clusters was conducted by infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD), showing the clusters molecularly adsorbed and maintaining a sandwich structure on the substrate.

DOI： 10.1142/9781848162389_0016

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (bulletin of university, research institution)   Publisher：ナノ学会会  

CiNii Article

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：IEEE COMPUTER SOC  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：化学工業社  

CiNii Article

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Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：SPRINGER VERLAG  

Net absorptive CIDEP generation has been demonstrated on singlet molecular oxygen and 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyl (OTEMPO) radical system in benzene. CIDEP generation was reasonably explained in terms of the radical-triplet pair mechanism of triplet molecular oxygen-OTEMPO pair with doublet precursor. Several excited molecule-OTEMPO systems have been investigated if this CIDEP generation contributes to their CIDEP spectra. Surprisingly strong CIDEP was produced even in the presence of trace amount of dissolved oxygen, which suggests the importance of complete degassing for CIDEP studies in general systems.

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Author：Myself 

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