Enhancement of Visible Light Response of TiO2 Photocatalyst by 3D-Deposited Ag Nanowires and Its Charge Separation Mechanism

In 3D-deposited AgNW/TiO2, which is prepared by spray-applying titanium dioxide suspension to deposited silver nanowire sheets, the synergistic effects of increased crossing points of AgNWs to enhance localized surface plasmon resonance excitation and longer-lived electrons in the conduction band of TiO2 generated by plasmon-induced charge transfer have successfully resulted in photocatalytic activity in the visible light range. We have developed photocatalytic sheets in which TiO2 particles are uniformly attached to 3D-deposited AgNWs. Regarding the prepared sheet, it was confirmed that TiO2 was indeed well adhered to the AgNWs, and electron transfer was efficient at the interface. This sheet solves the problem that the response wavelength range of the photocatalytic reaction using TiO2 is only in the ultraviolet region and exhibits sufficient photocatalytic effect in the visible light region. Transient absorption spectroscopy measurements in the diffuse reflectance configuration confirmed that the electrons of AgNWs actually move into the conduction band of TiO2 under visible light and that the interaction is independent of the excitation light intensity, thereby extending the lifetime of the electrons.


Blue Luminescent Boron Complexes Based on N,N-Type Imidazo[1,5-a]pyridine Ligand for Mitochondrial Imaging


Fabrication of MoO3/rGO/Au composite for increased photocatalytic degradation of methylene blue

International Journal of Modern Physics B


Photogenerated Carrier Dynamics of Mn2+ Doped CsPbBr3 Assembled with TiO2 Systems: Effect of Mn Doping Content

In recent years, all-inorganic perovskite materials have become an ideal choice for new thin film solar cells due to their excellent photophysical properties and have become a research hotspot. Studying the ultrafast dynamics of photo-generated carriers is of great significance for further improving the performance of such devices. In this work, we focus on the transient dynamic process of CsPbBr3/TiO2 composite systems with different Mn2+ doping contents using femtosecond transient absorption spectroscopy technology. We used singular value decomposition and global fitting to analyze the transient absorption spectra and obtained three components, which are classified as hot carrier cooling, charge transfer, and charge recombination processes, respectively. We found that the doping concentration of Mn2+ has an impact on all three processes. We think that the following two factors are responsible: one is the density of defect states and the other is the bandgap width of perovskite. As the concentration of doped Mn2+ increases, the charge transfer time constant shows a trend of initially increasing, followed by a subsequent decrease, reaching a turning point. This indicates that an appropriate amount of Mn2+ doping can effectively improve the photoelectric performance of solar cell systems. We proposed a possible charge transfer mechanism model and further elucidated the microscopic mechanism of the effect of Mn2+ doping on the interface charge transfer process of the CsPbBr3/TiO2 solar cell system.


Laser ablation synthesis of BiOCl/Ag/WO3 nanocomposite to evaluate its photocatalysis performance


Improved photocatalytic activities of TiO2/MoO3/Au nanocomposite prepared by hydrothermal method


Ternary composite WS2/GO/Au synthesized from laser ablation and hydrothermal method for photo- and electro-chemical degradation of methylene blue dye


Development of silver nanocubes created by pulsed laser ablation in liquid


Photocatalytic studies of tin oxide nanostructures produced by different methods


Tungsten suboxide (WO3x) petal-like nanosheets created by laser ablation method


Intramolecular Singlet Fission in Pentacene Oligomers via an Intermediate State

Intramolecular singlet fission (iSF) is an efficient strategy of multiexciton generation via a singlet exciton splitting into a correlated triplet pair in one organic molecule with more than two chromophores. Propeller-shaped iptycene-linked triisopropylsilyl(TIPS)-ethynyl functionalized pentacene oligomers (pent-monomer, pent-dimer, and pent-trimer) were synthesized, and the iSF dynamics of pent-dimer and -trimer were monitored by a visible-near-IR transient absorption (TA) spectroscopy. Quantum yields of the triplet pair, ∼80%, of both estimated by near-IR TA spectral analysis are in good agreement with the results of global analysis and triplet sensitization experiments. The iSF rate of pent-trimer is slightly faster than that of pent-dimer even with one more chromophore site. The unexpectedly weak difference indicates the existence of an intermediate process to realize iSF. The intermediate process might be determined by through-bond electronic coupling of the homoconjugation bridge in the pentacene oligomers. Our results suggest the importance of the rigid bridge to the fast iSF rate and the elongated lifetime of the correlated triplet pair in pentacene oligomers.


Observation of energy transfer dynamics in a phycocyanin protein crystal by utilizing femtosecond transient absorption microscopy


Observation of carrier dynamics in MoS2 thin layer by femtosecond transient absorption microscopy


Observation of electronic spectra modulation in a CH3NH3PbBr3 crystal by utilizing transient absorption microscopy


Basic aspects of gold nanoparticle photo-functionalization using oxides and 2D materials: Control of light confinement, heat-generation, and charge separation in nanospace

Although the optical properties of localized surface plasmon resonance and the relaxation processes of excited hot electrons in gold nanoparticles (AuNPs) have been well understood, the phenomena that occur when AuNPs relax on solid surfaces of semiconductors or insulators remain largely unknown. Thermal energy diffusion and electron transfer are relatively simple physical processes, but the phenomena they induce are interesting because of a variety of new application developments. In this Perspective, we introduce the fundamental aspects as well as advanced applications of several new physical phenomena induced by AuNPs-based hybrid materials with oxides or 2D materials. Localized heat can induce a great force on the surrounding medium to control mass transport, and plasmon-induced charge transfer reactions are expected to have applications in photocatalysis and solar cells. We also review increasing reports on the development of nano-optical sensors, transistors, and nano-light sources based on precisely controlled device structures utilizing AuNPs.


Creation of three dimensional octahedral tin oxide nanostructure produced by laser ablation in liquid


Effect of Phenolic Substituent Position in Boron Complexes of Imidazo[1,5-a]pyridine


Polymorph-Derived Diversification of Crystal Actuation by Photoisomerization and the Photothermal Effect


Two-photon excitable boron complex based on tridentate imidazo[1,5-a]pyridine ligand for heavy- atom-free mitochondria-targeted photodynamic therapy


Laser assisted synthesis of WS2 nanorods by pulsed laser ablation in liquid environment

International Journal of Modern Physics B


Photothermally Driven High-Speed Crystal Actuation and Its Simulation

Mechanically responsive crystals have been increasingly explored, mainly based on photoisomerization. However, photoisomerization has some disadvantages for crystal actuation, such as a slow actuation speed, no actuation of thick crystals, and a narrow wavelength range. Here we report photothermally driven fast-bending actuation and simulation of a salicylideneaniline derivative crystal with an -amino substituent in enol form. Under ultraviolet (UV) light irradiation, these thin (<20 μm) crystals bent but the thick (>40 μm) crystals did not due to photoisomerization; in contrast, thick crystals bent very quickly (in several milliseconds) due to the photothermal effect, even by visible light. Finally, 500 Hz high-frequency bending was achieved by pulsed UV laser irradiation. The generated photothermal energy was estimated based on the photodynamics using femtosecond transient absorption. Photothermal bending is caused by a nonsteady temperature gradient in the thickness direction due to the heat conduction of photothermal energy generated near the crystal surface. The temperature gradient was calculated based on the one-dimensional nonsteady heat conduction equation to simulate photothermally driven crystal bending successfully. Most crystals that absorb light have their own photothermal effects. It is expected that the creation and design of actuation of almost all crystals will be possible via the photothermal effect, which cannot be realized by photoisomerization, and the potential and versatility of crystals as actuation materials will expand in the near future.

Journal of the American Chemical Society


Charge separation dynamics in In2Se3/ZnO/Au ternary system for enhanced photocatalytic degradation of methylene blue under visible light

Journal of Photochemistry and Photobiology A: Chemistry


Vibrational decoherence induced by ultrafast intramolecular charge separation of an asymmetric bianthryl derivative

Coherent wavepacket oscillation accompanying the ultrafast photoexcited intramolecular charge separation (CS) of 9,9'-bianthryl (BA) and 10-cyano-9,9'-bianthryl (CBA) in a room temperature ionic liquid, N,N-diethyl-N-methyl-N-(methoxyethyl)ammonium tetrafluoroborate (DemeBF), was investigated by femtosecond time-resolved transient absorption spectroscopy. The frequency of the coherent oscillation observed for CBA in nonpolar n-hexane solution (Hex) was 377 cm, while this oscillation was undetectable in DemeBF. For BA in DemeBF, coherent oscillation with a frequency of 394 cm was observed, which is similar to that for CBA in Hex. CS of CBA occurs in the ultrashort time range of ≤100 fs, while that of BA occurs in a few picosecond range [E. Takeuchi et al., J. Phys. Chem. C 120, 14502-14512 (2016)]. Hence, the oscillation of CBA in Hex and that of BA in DemeBF are assigned to the molecular vibration in the locally excited state, while this oscillation dephases instantaneously for CBA in DemeBF due to the ultrafast CS and no oscillation was generated in the CS state. This result suggests that the CS reaction is not mediated by a specific intramolecular vibration in the CS state but occurs incoherently through higher levels of multiple vibrational modes.


Ultrafast and Hot Electron Transfer in CdSe QDAu Hybrid Nanostructures


Semiconductive Nature of Lead-Based MetalOrganic Frameworks with Three-Dimensionally Extended Sulfur Secondary Building Units


Quasi-Type II Carrier Distribution in CdSe/CdS Core/Shell Quantum Dots with Type I Band Alignment


Unravelling the Ultrafast Exciton Relaxation and Hidden Energy State In CH3NH3PbBr3 Nanoparticles


Cycloreversion Reaction of a Diarylethene Derivative at Higher Excited States Attained by Two-Color Two-Photon Femtosecond Pulsed Excitation.

Two-color, two-pulse femtosecond pulsed excitation was applied to the elucidation of the dynamics and mechanism of cycloreversion reaction of a diarylethene derivative in the higher excited states. Transient absorption spectroscopy under one-photon visible excitation revealed that the 1B state produced by the excitation undergoes the internal conversion into the 2A state with a time constant of 200 fs. Geometrical rearrangement of the 2A state takes place concomitantly with the vibrational cooling with a time constant of 3 ps. The resultant 2A state undergoes the transition into the conical intersection point in competition with nonradiative as well as radiative deactivation into the ground state with a time constant of 12 ps. The second pulse excitation of the 2A state, especially the geometrically relaxed 2A state, led to the significant enhancement of the cycloreversion reaction through the large reaction quantum yield of ca. 50-90% in the higher excited state (S state), while the excitation of the 1B state, leading to the S' state, did not induce such enhancement. By integrating with the excitation wavelength dependence of the second pump laser pulse, we discussed the chemical reactivity of diarylethene derivatives in terms of the symmetry of the electronic states.


Femtosecond Excited-State Dynamics of Fullerene-C60 Nanoparticles in Water.

Femtosecond excited-state dynamics of fullerene-C nanoparticles (nC) having a mean size of 50 nm dispersed in pure water was studied by means of femtosecond transient absorption spectroscopy. The intermolecular charge-transfer (CT) excited state in solid C was directly and firstly observed by femtosecond 350 nm and 420 nm excitations, and its intrinsic lifetime of 0.35 ps was found. The CT excited state relaxed to the locally excited S state and excimers or directly to the ground state through geminate charge recombination. We also examined the laser fluence dependence of the CT excited-state dynamics. At a high laser fluence, the mutual interactions between neighboring CT excited states were observed immediately after the excitation. The interaction disappeared through the charge recombination in the geminate CT pair or between the neighboring CT excited states with a lifetime of 0.45 ps. After that, the locally excited S state decayed with a few ps lifetime independent of the fluence. In this paper, the mechanism and dynamics of the intermolecular CT excited state generated by UV light excitation is discussed in detail.


Solid-Solution Coordination Polymers as Precursors for ZnxCd1-xS/C Composite Nanowires.


Dynamics of Excitation Energy Transfer Between the Subunits of Photosystem II Dimer.

Energy transfer dynamics in monomer and dimer of the photosystem II core complex (PSII-CC) was investigated by means of femtosecond transient absorption (TA) spectroscopy. There is no profound difference between the TA dynamics of the monomer and the dimer in the weak excitation intensity condition (≤21 nJ). However, the fast recovery of the ground state bleach was pronounced at higher excitation intensities, and the excitation intensity dependence of the dimer was more significant than that of the monomer. This result indicates efficient exciton-exciton annihilation taking place in the dimer due to energy transfer between the two monomer units. The annihilation dynamics was reproduced by a simple model based on binomial theorem, which indicated that although PSII-CC dimer has two reaction centers, only one charge-separated state remained after annihilation.


Sub-100 fs Charge Separation and Subsequent Diffusive Solvation Observed for Asymmetric Bianthyril Derivative in Ionic Liquid


Stepwise Two-Photon-Induced Fast Photoswitching via Electron Transfer in Higher Excited States of Photochromic Imidazole Dimer.

Stepwise two-photon excitations have been attracting much interest because of their much lower power thresholds compared with simultaneous two-photon processes and because some stepwise two-photon processes can be initiated by a weak incoherent excitation light source. Here we apply stepwise two-photon optical processes to the photochromic bridged imidazole dimer, whose solution instantly changes color upon UV irradiation and quickly reverts to the initial color thermally at room temperature. We synthesized a zinc tetraphenylporphyrin (ZnTPP)-substituted bridged imidazole dimer, and wide ranges of time-resolved spectroscopic studies revealed that a ZnTPP-linked bridged imidazole dimer shows efficient visible stepwise two-photon-induced photochromic reactions upon excitation at the porphyrin moiety. The fast photoswitching property combined with stepwise two-photon processes is important not only for the potential for novel photochromic materials that are sensitive to the incident light intensity but also for fundamental photochemistry using higher excited states.

Journal of the American Chemical Society


Laser-driven phase transitions in aqueous colloidal gold nanoparticles under high pressure: Picosecond pump-probe study

Pump-probe transient extinction spectroscopy was applied to analyze 355-nm picosecond laser heating-induced phenomena of 60-nm-diameter aqueous gold nanoparticles (AuNPs) under a high pressure of 60 MPa. Kinetic spectroscopy revealed that a supercritical layer surrounding the AuNP nucleated with a lifetime of approximately 1 ns in its dynamic expansion and decay behavior for a fluence of 19.6 mJ cm 2. Moreover, we observed in the post-mortem transmission electron micrographs a number of fragments, a small percentage of size-reduced cores, and erupted particles, among the intact particles after 60 shots, suggesting that evaporation occurs under laser illumination. The particle temperature calculation indicated that evaporation begins with a liquid droplet AuNP surrounded by a supercritical layer at temperatures below the boiling point of gold. By applying high pressure, we are able to obtain a clear picture of the evaporation event, which was not possible at ambient pressure because the forming bubble caused particle temperatures to rise uncontrollably. In this study, we shed light on the critical role of the supercritical layer formed around the AuNP under high pressure during laser-induced evaporation.


Solvent Polarity Dependence of Photochromic Reactions of a Diarylethene Derivative as Revealed by Steady-State and Transient Spectroscopies.


Extension of Light-Harvesting Ability of Photosynthetic Light-Harvesting Complex 2 (LH2) through Ultrafast Energy Transfer from Covalently Attached Artificial Chromophores.

Introducing appropriate artificial components into natural biological systems could enrich the original functionality. To expand the available wavelength range of photosynthetic bacterial light-harvesting complex 2 (LH2 from Rhodopseudomonas acidophila 10050), artificial fluorescent dye (Alexa Fluor 647: A647) was covalently attached to N- and C-terminal Lys residues in LH2 α-polypeptides with a molar ratio of A647/LH2 ≃ 9/1. Fluorescence and transient absorption spectroscopies revealed that intracomplex energy transfer from A647 to intrinsic chromophores of LH2 (B850) occurs in a multiexponential manner, with time constants varying from 440 fs to 23 ps through direct and B800-mediated indirect pathways. Kinetic analyses suggested that B800 chromophores mediate faster energy transfer, and the mechanism was interpretable in terms of Förster theory. This study demonstrates that a simple attachment of external chromophores with a flexible linkage can enhance the light harvesting activity of LH2 without affecting inherent functions of energy transfer, and can achieve energy transfer in the subpicosecond range. Addition of external chromophores, thus, represents a useful methodology for construction of advanced hybrid light-harvesting systems that afford solar energy in the broad spectrum.


Cooperative conformational change and excitation migration of biphenyl-PMO amorphous film, as revealed by femtosecond time-resolved spectroscopy.


Picosecond-to-Nanosecond Dynamics of Plasmonic Nanobubbles from Pump-Probe Spectral Measurements of Aqueous Colloidal Gold Nanoparticles --- 金ナノ粒子コロイド溶液にパルスレーザーを照射することによって発生する蒸気バブルの過渡スペクトルをピコ秒時間分解で測定した．Mie理論を用いたシミュレーションにより，バブルの発生による周囲屈折率の低下およびバブルの成長による散乱断面積の増加により，スペクトルが時間喧嘩する様子をシミュレーションし，実験結果とよく一致することを示した．実験結果に基づいて，バブルの生成，成長，崩壊をバブルの直径の時間変化で表した．

The photothermal generation of nanoscale vapor bubbles around noble metal nanoparticles is of significant interest, not only in understanding the underlying mechanisms responsible for photothermal effects, but also to optimize photothermal effects in applications such as photothermal cancer therapies. Here, we describe the dynamics in the 400 900-nm regime of the formation and evolution of nanobubbles around colloidal gold nanoparticles using picosecond pump-probe optical measurements. From excitations of 20 150-nm colloidal gold nanoparticles with a 355-nm, 15-ps laser, time-dependent optical extinction signals corresponding to nanobubble formation were recorded. The extinction spectra associated with nanobubbles of different diameters were simulated by considering a concentric spherical core-shell model within the Mie theory framework. In the simulations, we assumed an increase in particle temperature. From temporal changes in the experimental data of transient extinctions, we estimated the temporal evolution of the nanobubble diameter. Corrections to bubble-free temperature effects on the transient extinction decays were applied in these experiments by suppressing bubble formation using pressures as high as 60 MPa. The results of this study suggest that the nanobubbles generated around a 60-nm-diameter gold nanoparticle using a fluence of 5.2 mJ cm-2 had a maximum diameter of 260 ± 40 nm, and a lifetime of approximately 10 ns. The combination of fast transient extinction spectral measurements and spectral simulations provides insights into plasmonic nanobubble dynamics.


Inhomogeneous deactivation process with UV excitation in submicron grains of lead iodide perovskite-based solar cell as revealed by femtosecond transient absorption microscopy.


Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pumpprobe spectroscopy


The Effect of Pre-solvation in the Ground State on Photoinduced Electron Transfer in Ionic Liquids


Constraint-induced structural deformation of planarized triphenylboranes in the excited state.


Mechanistic studies of photoinduced intramolecular and intermolecular electron transfer processes in RuPt-centred photo-hydrogen-evolving molecular devices.


Photoinduced charge-transfer dynamics of sequentially aligned donoracceptor systems in an ionic liquid

Photochemical & Photobiological Sciences


Dynamics Photochemistry of fac-Re(bpy)(CO)3Cl.


Photoswitchable fluorescent diarylethene derivatives with short alkyl chain substituents.

The sulfone derivatives of 1,2-bis(2-alkyl-6-phenyl-1-benzothiophen-3-yl)perfluorocyclopentene having various short alkyl chain substituents at reactive carbons were prepared and the effect of alkyl substitution on the fluorescence property of the closed-ring isomers was studied. Upon irradiation with ultraviolet (UV) light the derivatives exhibit a brilliant green fluorescence under irradiation with visible (> 400 nm) light, while the fluorescence disappears upon irradiation with visible (> 400 nm) light alone. The fluorescence quantum yield of the methyl substituted derivative (1b) dramatically decreases from 0.84 to 0.15 when the solvent is changed from hexane to acetonitrile, while the changes of ethyl, n-propyl and n-butyl substituted derivatives (2b)-(4b) are moderate. The quantum yields of (2b)-(4b) are kept to values close to 0.7 even in polar acetonitrile. The fluorescence lifetime measurement revealed that efficient non-radiative decay processes took place in (1b) in polar solvent, while their contribution to the deactivation was not so large in (2b)-(4b). The neighboring short alkyl chains at the connecting carbons are considered to defend the sulfone units against the attack of polar solvent molecules and weaken the solvent polarity effect.


Excited-state Dynamics of Fullerene Nanoparticles Dispersed in Pure Water.

Femtosecond transient absorption dynamics of C60 nanoparticles in pure water revealed a strong quenching of the singlet excited state, independent of the excitation light intensity on a 10-ps time scale, and an extremely low yield of the triplet state of C60 nanoparticles upon photoexcitation.


Direct detection of Electron Transfer Processes in Photoconductive Poly(N-vinylcarbazole) Solid Film Doped with Electron Acceptors: Temperature Dependence of Femtosecond to Microsecondmics.

Journal of Photochemistry and Photobiology A: Chemistry


Norharmane: Old yet highly selective dual channel ratiometric fluoride and hydrogen sulfate ion sensor.


Coherent dynamics and ultrafast excited state relaxation of blue copper protein; plastocyanin.

Ultrafast transient absorption measurements in the femtosecond to picosecond time region were carried out for a blue copper protein, plastocyanin (Pc). To compare the dynamical profiles after photoexcitation upon the ligand-to-metal-charge-transfer (LMCT) band and the d-d transition band, the pump wavelength was set at wavelengths of 597 and 895 nm, respectively. The results were nearly identical, indicating that the transition from the LMCT to the lower ligand field (LF) states takes place in an ultrafast time regime of less than 40 fs. Subsequently, relaxation in the LF state occurs with a time constant of 90 fs and the system returns to the ground state with that of 250 fs. The longest time constant of 1.8 ps was attributed to the vibrational cooling in the ground state. Several wavepacket motions were observed, including Franck-Condon type motion at approximately 510 nm and a Herzberg-Teller type motion at 660-720 nm. Critically damped low-frequency oscillation of approximately 30 cm(-1) was also observed with both excitation wavelengths with the strongest amplitude around 600 nm. This oscillation could be due to the motion of the protein that is ballistically stimulated by ultrafast relaxation.


Fluorescence photoswitching of a diarylethene-perylenebisimide dyad based on intramolecular electron transfer.


Multiphoton-gated cycloreversion reactions of photochromic diarylethene derivatives with low reaction yields upon one-photon visible excitation.


Ultrafast delocalization of cationic states in poly(N-vinylcarbazole) solid leading to carrier photogeneration

Femtosecond measurements of the transient dichroism and near-IR time-resolved spectra revealed the ultrafast delocalization of the cationic state in poly(N-vinylcarbazole), leading to carrier photogeneration.


Ultrafast Laser Spectroscopic Study on Photochromic Cycloreversion Dynamics in Fulgide Derivatives: One-Photon and Multiphoton-Gated Reactions


Photoisomerization of Azobenzene Gel by Pulsed Laser Irradiation


Synthesis of blue luminescent boron complex of 3-(o-hydroxyphenyl)imidazo[1,5-a]pyridine

Proceedings of the LED General Forum 2022 Tokushima


Photodimers of symmetrical tetraaryl[3]cumulenes showing crystallization-induced emission enhancement nature


Energy Transfer between Subunits of Photosystem II Dimer Observed by Femtosecond Transient Absorption.

Optics InfoBase Conference Papers, International Conference on Ultrafast Phenomena 2016


Ultrafast Energy Transfer in LH2 Photosynthetic Antenna Conjugated with Artificial Fluorescent Dyes

Optics InfoBase Conference Papers, International Conference on Ultrafast Phenomena 2014


Ultrafast Intramolecular Charge Transfer Process of Asymmetric 9,9-Bianthryl derivative in Ionic Liquid


Coherent nuclear motions of blue copper protein, plastocyanin: comparing LMCT and d-d Excitation

Optics InfoBase Conference Papers, International Conference on Ultrafast Phenomena 2010