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Development of two-dimensional materials and exploration of their functionalities are significant challenges due to their potential. In this study, we successfully fabricated a supramolecular nanosheet composed of amphiphilic Rose Bengal dyes in an aqueous medium. Furthermore, we elucidated a distinct change in the photosensitisation mechanism induced by nanosheet formation.

We demonstrate that polymer dots doped with thermally activated delayed fluorescence (TADF) molecules clearly exhibit blue radio-luminescence upon hard X-ray and electron beam irradiation, which is a new design for nano-sized scintillators., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this study, we synthesized radioexcitable luminescent polymer dots (P-dots) doped with heteroleptic tris-cyclometalated iridium complexes that emit red, green, and blue light. We investigated the luminescence properties of these P-dots under X-ray and electron beam irradiation, revealing their potential as new organic scintillators., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Nitric oxide (NO) is a signaling molecule that plays a variety of functions in the human body, but it is difficult to use it in biological experiments or for therapeutic purposes because of its high reactivity and instability in the biological milieu. Consequently, photocontrollable NO releasers, which enable spatiotemporal control of NO release, have an important role in elucidating the functions of NO. Our group has developed visible-light-controllable NO-releasing molecules that contain a fluorescent dye structure as a light-harvesting antenna moiety and an N -nitrosoaminophenol structure as an NO-releasing moiety. Here, we aimed to construct an NO-generating system employing an intermolecular photoredox reaction between the two separate components, since this would simplify chemical synthesis and make it easier to examine various dyes as antennae. For this purpose, we constructed polymer nanoparticles doped with both N -methyl- N -nitroso-4-aminophenol (NAP, 1) and an Ir(III) antenna complex (2, 3 or 4) in order to dissolve in aqueous solution without a co-solvent. These polymer nanoparticles released NO upon photoirradiation in vitro in the purple (400-430 nm) or blue (400-460 nm) wavelength region to activate the doped Ir(III) complex.

Diaryldisulfides are known to undergo S-S bond cleavage upon one-electron reduction, which is called mesolysis of radical anions, to form the corresponding arylthiyl radical and anion. In this study, we prepared (4-cyanophenyl)(4'-methoxyphenyl)disulfide (MeOSSCN), and the mesolytic profiles were investigated by γ -ray and pulsed-electron radiolyses in 2-methyltetrahydrofuran. As a result of radiolysis of MeOSSCN at room and lower temperatures, the formation of the methoxythiyl radical was recognized upon mesolysis of the radical anion. This observation indicated that intramolecular electron transfer in the radical anion occurred, and the stepwise mechanism was operative after the attached electron occupied the antibonding σ*-orbital for promoting the S-S bond cleavage. According to the Arrhenius expression for the decay rates of the radical anion, the activation energy and frequency factor were determined. DFT calculations provided the bond dissociation energy and bond length for the S-S bond and charge distribution on the S atoms in the radical anion. The substituent effects on the mesolysis process are discussed.

Porphyrin covalent organic nanodisks (CONs) were synthesized by exfoliating covalent organic frameworks (COFs) in acidic aqueous solutions at pH 4. The synthesized CONs showed remarkable bactericidal activity against Escherichia coli owing to enhanced generation of singlet oxygen upon visible light irradiation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report the aggregation-induced photosensitizing activity of a cyanine dye in water and the mechanism. In addition, using the supramolecular assembly, visible-light-driven photooxidation of hydrophobic aromatic compounds in water was successfully performed.

Photocatalysis holds great potential in alleviating the growing energy crisis and environmental issues. Defect engineering has been demonstrated as an effective method to modulate the electronic structure of semiconductor photocatalysts for enhanced visible light absorption. However, the effect of defects on photocatalytic activity is still under debate because of the elusive charge transfer process mediated by defects. In this feature article, we summarize our recent progress in unraveling the defect-mediated electron transfer of the widely studied TiO 2 and polymeric carbon nitride photocatalysts by combining ultrafast time-resolved spectroscopy and theoretical simulations. We find that the photogenerated electron transfer is greatly dependent on the type and concentration of defects. The location and occupation of defect states, and the dispersion degree of the energy band should be carefully tuned to maximize the advantages of defects for photocatalytic reactions.

A B 12 complex-BODIPY dyad was synthesized by peripheral modification of cobalamin derivatives. The photophysical properties of the dyad were investigated by UV-vis, PL, and transient absorption spectroscopy. A visible light-driven dechlorination reaction of a trichlorinated organic compound, DDT, was reported. The dyad showed efficient catalysis for dechlorination under N 2 with turnover numbers of over 220 for the reaction. One-pot syntheses of an ester and amide from DDT and benzotrichloride were also achieved using the dyad under air.

The development of photocatalysts is an essential task for clean energy generation and establishing a sustainable society. This paper describes the aggregation-induced photocatalytic activity (AI-PCA) of amphiphilic rhodamines and photocatalytic functions of the supramolecular assemblies. The supramolecular assemblies consisting of amphiphilic rhodamines with octadecyl alkyl chains exhibited significant photocatalytic activity under visible light irradiation in water, while the corresponding monomeric rhodamines did not exhibit photocatalytic activity. The studies on the photocatalytic mechanism by spectroscopic and microscopic analyses clearly demonstrated the AI-PCA of the rhodamines. Moreover, the supramolecular assemblies of the rhodamines exhibited excellent photocatalytic hydrogen evolution rates (up to 5.9 mmol g -1 h -1 )., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We investigate the photogenerated electron kinetics of a thermal-decomposed polymeric carbon nitride (TCN) synthesized in air using femtosecond time-resolved diffuse reflectance spectroscopy. We find that the oxygen functional groups in TCN contribute to the formation of reactive shallow trap states for photogenerated electrons, leading to an enhanced activity for photocatalytic hydrogen evolution.

Hard X-ray excited optical luminescence is a unique property of materials, which makes them promising for biological imaging applications. However, the preparation of biocompatible contrast agents for hard X-ray excited optical luminescence remains a considerable challenge that has, to date, not been overcome. In this study, we investigated the luminescence properties of protein-directed Au ∼20 clusters upon hard X-ray irradiation, both in solution and when embedded in films., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Au TNP/g-C 3 N 4 as a plasmonic photocatalyst for H 2 production under NIR light irradiation was investigated by finite-difference time-domain (FDTD) simulations and time-resolved transient absorption measurements, revealing enhanced H 2 production owing to a stronger electromagnetic field in Au TNP/g-C 3 N 4 and plasmon-induced hot electron transfer from Au TNPs to g-C 3 N 4 .

The introduction of nitrogen (N) defects (N vacancies labeled as Vns and cyano groups) has been demonstrated as one of the promising strategies to extend the light absorption range of graphitic carbon nitride (CN), thus improving the photocatalytic activity for hydrogen (H2) evolution. However, the photocatalysis mechanism of such N-deficient CN (DCN) has not been fully understood. In this study, N defects are introduced into CN by a KOH-assisted thermal polymerization method. On the basis of experimental investigations and density functional theory (DFT) calculations, it is found that the extension of the absorption range of DCN is attributed to both the valence band (VB) tailing induced by Vns and bandgap narrowing induced by cyano groups. Moreover, the conduction band (CB) is lowered by the N defects, indicating a reduced driving force for H2 evolution. Transient absorption (TA) spectroscopy reveals that when the electrons in the intrinsic VB of DCN are excited to the CB, the separation efficiency of these electrons and as-generated holes is seriously restricted by their low mobility. While when the electrons in VB tail states (Vn states) are excited to the CB, the separation efficiency of these electrons and as-generated holes could be almost maintained thanks to the improved mobility of the holes. As a result, DCN shows a limited enhancement of the H2 evolution rate compared with CN under visible light irradiation. This work points out that extending the light absorption range of a given photocatalyst by doping (or self-doping) may be accompanied by some negative factors, which restrict the overall photocatalytic activity.

Hoop-shaped macrocycles such as cycloparaphenylenes ([n]CPPs, where n denotes the number of phenylene rings) have attracted considerable attention in recent years because of their interesting properties arising from the highly strained aromatic structure and radially oriented p-orbitals. While the radical cation and dication states of [n]CPPs have been characterized, there is no information available about their excited states, which are expected to exhibit enhanced redox properties. In this study, we investigated the S1 state of [n]CPP2+ by transient absorption measurements in the visible and near-IR regions. The energy of the transient absorption peak exhibited a linear relationship with the reciprocal of the repeating unit, which indicated that the distribution of the excited state expanded with the size of the ring. In addition, smaller CPP2+s showed longer excited state lifetimes. Theoretical calculations suggested that there was a substantial structural relaxation of the smaller CPP2+s accompanying the changes in the charge distribution. Therefore, it was concluded that the smaller Franck-Condon factor resulting from the considerable structural change and larger S1 energy were responsible for the longer S1 state lifetime of smaller CPP2+s.

We investigated Au/TiO2 mesocrystals as plasmonic photocatalyst prototypes using single-particle photoluminescence (PL) spectroscopy combined with finite-difference time-domain (FDTD) simulations, and found that introduction of defect states builds up a channel for hot electrons with energies lower than the Schottky barrier height to transfer to the semiconductor.

We propose a new sensor design that maximizes fluorescence contrast, inspired by whispering-gallery mode lasing (WGM). Aptamer-modified glass microspheres ( cf. 1-38 μm) and thrombin are used as a model sensory cavity and target protein, respectively. Two types of microsphere are prepared to compare fluorescence contrast: turn-on and turn-off types by using fluorophore-labeled target protein and fluorophore-labeled DNA duplex with thrombin-binding aptamer (TBA), respectively. For the turn-on type, a fluorescence increase was detected in the presence of 100 nM thrombin, but signal amplification upon excitation power did not occur. As for the turn-off type, in the absence of thrombin, fluorophores are densely populated around the microsphere, leading to fluorescence confinement and intensity amplification upon increasing the pump intensity. By adding thrombin, a complementary strand of TBA is dissociated from the microsphere, and the G-quadruplex structure of the thrombin aptamer recognizes and binds to thrombin. As the fluorophore density around the microsphere decreases, fluorescence amplification based on WGM resonance is halted, resulting in 29-fold enhanced contrast under increased excitation power., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Herein, we investigated that sheet-like TiO 2 mesocrystals with controllable nanothorns on the {101} facet during the topotactic transformation exhibit facet-induced charge separation and anisotropic electron flow, realizing the superior facet-dependent photocatalysis in solar energy conversion.

In the past few decades, charge transfer in DNA has attracted considerable attention from researchers in a wide variety of fields, including bioscience, physical chemistry, and nanotechnology. Charge transfer in DNA has been investigated using various techniques. Among them, time-resolved spectroscopic methods have yielded valuable information on charge transfer dynamics in DNA, providing an important basis for numerical practical applications such as development of new therapy applications and nanomaterials. In DNA, holes and excess electrons act as positive and negative charge carriers, respectively. Although hole transfer dynamics have been investigated in detail, the dynamics of excess electron transfer have only become clearer relatively recently. In the present paper, we summarize studies on the dynamics of hole and excess electron transfer conducted by several groups including our own.

Since it was first reported in 2008, great attention has been paid to Si-rhodamine (SiR) because of its far-red to near-infrared (NIR) absorption/fluorescence and suitability for high-resolution in vivo imaging. However, properties of SiR in the excited state have not been reported, even though they are directly related to its fluorescence. In the present study, the properties of SiR monomers in the excited states are thoroughly characterized for the first time. Moreover, by replacing a phenyl moiety of SiR with a 4-(9-anthryl)phenylene group (SiR-An), we prepared H- and J-aggregates of SiR in the aqueous solution, and succeeded in monitoring exciton formation and annihilation in the aggregates. Interestingly, the relative exciton population in the SiR J-aggregate increases as the excitation power becomes stronger, which is unusual considering that the substantial exciton-exciton annihilation process occurs as more excitons are generated. The results obtained in the present study suggest high versatility of SiR not only as a red fluorophore in the cutting-edge microscopic techniques but also as a NIR absorber in the light harvesting system.

In the present study, electron transfer (ET) processes from excited radical anions have been investigated using dyad molecules including C60. The deactivation process of excited C60˙(-), including the internal conversion from the D1 to the D0 state and the cooling process of the vibrationally hot ground state (D), was observed spectroscopically for the first time. These processes could be unambiguously distinguished by the observation of the stimulated emission from the D1 state. The intramolecular ET processes from the excited C60˙(-) were confirmed by the transient absorption spectra. Clearly, both D1 and D states acted as precursors for the ET, i.e., dual ET pathways were confirmed. The driving force dependence of the ET rates was well characterized by the Marcus theory, which revealed that the forward ET processes are located at the top region of the Marcus parabola. In addition, the ET from the excited imide radical anion to C60 and that from the ground state C60˙(-) to imide were examined. The ET rate from the excited imide radical anion and that from ground state C60˙(-) did not follow the Marcus parabola estimated for the ET from the excited C60˙(-). The observed difference can be attributed to the difference in the energy required to form the reduced spacer (Δ) in the superexchange mechanism. Because the Δ value tends to become smaller for ET processes from excited radical ions, fast and efficient ET processes are expected from these states as demonstrated in the present study.

We report a substitution of 9-phenylanthracenyl group into rhodamine derivatives that can induce the J-aggregate formation of rhodamine moieties in the aqueous solution upon the addition of a halide ion. From X-ray crystallographic analysis, the dramatic red-shift in the absorption band (i.e. app. 100 nm) originates from the cooperative slipped-stacking of rhodamine and anthracene molecules.

Here we demonstrated that 3D architectures of TiO2 mesocrystals uniformly packed with a chemically exfoliated MoS2 shell exhibit promising reactive efficiency and good stability in synergetic hydrogen evolution. The efficient interfacial electron transfer from the excited TiO2 moieties to the decorated ultrathin MoS2 shell was effectively monitored.

Although the folding kinetics of cytochrome c (Cyt-c), ferric or ferrous Cyt-c, has been extensively investigated as a paradigm for a protein folding reaction using various time-resolved spectroscopic techniques, the configurational change of heme associated with the folding reaction from a ferric Cyt-c to a ferrous Cyt-c induced by one-electron reduction has not been elucidated. To address this issue, we investigated the configurational change of heme in the Cyt-c folding process induced by one-electron reduction using a combination of time-resolved resonance Raman spectroscopy and pulse radiolysis. The results presented herein reveal that the reduction of ferric Cyt-c and the ligation of Met80 occur simultaneously within a timescale of approximately 2 μs, and that the ligand binding and exchange of heme depend on the initial configuration of the heme. The rapid ligation of Met80 observed in this study may be attributed to the intramolecular diffusion of Met80 into ferrous Cyt-c with a 5-coordinated high-spin configuration. Conversely, the ligand exchange of a ferrous Cyt-c with a 6-coordinated low-spin configuration was significantly slower.

This study examines the effects of cyclodextrin (CD) on the photophysical properties of 1,8-naphthalimide (NI) derivatives including NI-linker-phenothiazine (NI-L-PTZ) dyads in a H2O/CH3CN solution (v/v = 9 : 1). Peculiar excimer and exciplex emissions were observed with reference NI and NI-L-PTZ, respectively, in an aqueous environment. The NI-CD complexes exhibited monomeric emission spectral features, which resulted from their inclusion into the CD cavity. The complex formation constants of CDs with the NI derivatives were determined. The T1-Tn absorption band of (3)NI* was observed at around 470 nm during nanosecond-laser flash photolysis. Photoinduced electron transfer in NI-L-PTZ led to NI˙(-) and PTZ˙(+) from the T1 state. In protic polar solvents, NI˙(-) easily formed a ketyl radical (NIH˙) by hydrogen abstraction from H2O, and showed a transient absorption band at around 400 nm. The charge recombination (CR) time of the transient species at 400 nm showed a strong CD dependency, and the CR time of the dyad in γ-CD was increased markedly compared with in β-CD. This suggests that the PTZ moiety can also be included in the γ-CD cavity.

Porphyrins have been used by various researchers as important building blocks of photofunctional molecules, while the number of studies on the excitation properties of the structural isomers of porphyrins is small when compared to those of porphyrins. In the present study, photoinduced electron transfer (ET) processes of supramolecular donor-acceptor dyads of 2,3,6,7,11,12,17,18-octaethylcorrphycenatozinc (ZnCn), one of the porphyrin isomers, and some imide compounds, which can coordinate to the central Zn ion as an electron acceptor, were investigated. Formation of the supramolecular donor-acceptor dyads was confirmed by steady state absorption change. Charge separation and charge recombination processes upon photoexcitation of ZnCn of the supramolecular dyads were successfully observed by subpicosecond laser flash photolysis. The estimated ET rates (kET) were compared with those of other porphyrin isomers. Differences in the driving force dependence of kET values of porphyrin isomers were attributed to the electronic coupling and internal reorganization energy. Electronic and structural factors, which brought about the difference in kET values, were reasonably explained on the basis of the theoretical calculation.

Excess electron transfer dynamics in DNA hairpins was investigated by femtosecond laser flash photolysis of a donor-DNA-acceptor system using N,N-dimethylaminopyrene and diphenylacetylene as an electron donor and acceptor, respectively. It was revealed that the excess electron hopping rate between T's is faster than that of the hole.

Hoop-shaped π-conjugated molecules such as cycloparaphenylene (CPP) have attracted the attention of many chemists because they exhibit interesting properties due to the distorted π-electron system. To gain a systematic understanding of the properties that result from distorted π-electron systems, it is important to know precisely how these properties depend on the hoop size. In the present study, we have investigated the size dependence of the fluorescence properties of CPPs. The fluorescence spectra of smaller CPPs showed red-shifted fluorescence peaks, smaller fluorescence quantum yields, and longer lifetimes, when compared to those of larger ones. One of the important factors that gave rise to these fluorescence properties of smaller CPPs was greater structural relaxation from the Franck-Condon state, which is a postulation supported by theoretical calculations. The structural relaxation in the picosecond domain was experimentally detected by the fluorescence upconversion method. The present results are an important example that confirms steric factors strongly governing the fluorescence properties of a molecule.

Charge transfer in DNA attracts substantial attention from researchers in a wide group of fields such as bioscience, nanotechnology and physical chemistry. It is well known that both positive and negative charges, which are holes and excess electrons, respectively, contribute to the charge transfer in DNA. In the case of hole transfer in DNA, detailed mechanisms and dynamical parameters have been estimated by means of time-resolved spectroscopic methods and product analysis. On the other hand, detailed dynamics of excess electron transfer have not been established yet, although several aspects have been revealed by the continuous efforts of various research groups. In the present Perspective, studies on the charge transfer dynamics in DNA are summarized.

Novel boron dipyrromethene (BODIPY) derivatives having significant absorption and emission in the longer wavelength region were synthesized. BODIPY showed anomalous S(2) emission from the second excited (S(2)) state at shorter wavelength. The photodynamics of the S(2) state was investigated by fluorescence up-conversion and transient absorption spectroscopic measurements. The decay time of the S(2) emission was dependent on the internal conversion and the intersystem crossing process. The assignments of transitions were supported by a theoretical calculation based on the time-dependent density functional theory., (This journal is © The Royal Society of Chemistry 2012)

Graphene oxide (GO) nanosheets have received a great deal of attention for a wide range of applications from optoelectronic devices to biological sensors. We now report a mechanistic study of the interfacial electron transfer (ET) processes between organic dye molecule, 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF), and nanometre-sized GO sheets using ensemble-averaged and single-molecule spectroscopies. The ET dynamics was characterized by the direct observation of the PF radical cation during the laser flash photolysis, and its reaction rate was determined to be ~10(11) s(-1). The single-molecule fluorescence spectroscopy was utilized to clarify the heterogeneous nature of the interfacial ET within individual composites. Their fluorescence lifetimes and spectra were found to vary from composite to composite, possibly due to the different local structures and molecular interactions. The autocorrelation analysis of fluorescence intensity trajectories also revealed the temporal fluctuation of the ET reactivity.

Denaturant-induced conformational change of yeast iso-1-cytochrome c (Cytc) has been comprehensively investigated in the single-molecule and bulk phases. By fluorescence-quenching experiments with dye-labelled heme-protein (Alexa 488-labelled Cytc, Cytc-A488), we clearly show that the fluorescence quenching observed from folded Cytc-A488 is due mainly to photoinduced electron transfer (PET) between electron-donating amino acids such as tryptophan and the dye attached to the protein. In addition, the unfolding process of Cytc-A488 observed in the single-molecule and bulk phases can be explained well in terms of a three-state model: Cytc unfolds through an intermediate with a native-like compactness. By quantitative analysis of fluorescence correlation spectroscopy (FCS) data, we were able to observe a relaxation time of ∼1.5 μs corresponding to segmental motion and fast folding dynamics of 55 μs in the unfolded state of Cytc. The results presented here also suggest that a combination of single-molecule and ensemble-averaged spectroscopy is necessary to provide convincing and comprehensive assignments of protein kinetics.

The study of the structural reorganization and photophysical properties of Zn-Cytc using the single-molecule and ensemble-averaged spectroscopy shows that the photoblinking behaviors of single-Zn-Cytc depend on the folded and unfolded structures, whereas the fluorescence dynamics of Zn-Cytc observed in the bulk phase are hardly affected by the conformational change of a protein.

Intramolecular dimer radical anions of [3n]cyclophanes generated by gamma-ray irradiation in low-temperature glassy matrices showed an absorption band attributable to charge resonance around 936-1210 nm, from which the stabilization energy of the dimer radical anions were analyzed on the basis of pi-electron delocalization over two benzene rings and the damping factor (beta) was estimated to be 0.35 A(-1), which is smaller than that of the intramolecular dimer radical cation of [3n]cyclophanes, indicating a effective charge delocalization of the dimer radical anions.

The intermolecular photoinduced electron transfer (PET) processes of 1,8-naphthalimide (NI) derivatives including NI-linker-phenothiazine dyads were investigated in a protic H(2)O/CH(3)CN (v/v=1:1) solvent using ns-laser flash photolysis with 355 nm-laser excitation. NI derivatives are surrounded by H(2)O in the ground state in H(2)O/CH(3)CN. The T(1)-T(n) absorption band of (3)NI* was observed at around 470 nm. The transient absorption band at around 410 nm increased concomitantly with the decay of (3)NI* in H(2)O/CH(3)CN. This implies that hydrated NI anion radical (NI*(-)) is primarily generated via the quenching of (3)NI* by NI at the diffusion control rate. This intermolecular PET did not occur in aprotic CH(3)CN. The formation and decay times of NI*(-) showed strong dependence on the concentration of NI. Then, we suggest that NI*(-) could undergo proton abstraction to give ketyl radical species of NI [NI(H)*] in H(2)O/CH(3)CN.

Transient absorption measurements of charge transfer (CT) demonstrated that the CT in the DNA assembly constructed by simply mixing DNAs with sticky ends occurs over 200 angstroms selectively to the complementary sticky end sequences.

Based on the synthesis of DNA modified with photosensitizers, direct spectroscopic measurements of the hole transfer in DNA, and quantification of the yield of the DNA oxidative damage, the reaction rate of the radical anion of the photosensitizer was demonstrated to be critically important in determining the efficiency of photosensitized DNA damage.

2-Aminopurine (Ap) modified human telomere sequences were used to monitor the specific complex formation of the G-quadruplex and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4).

The combination of the transient absorption measurement and DNA damage quantification by HPLC clearly demonstrated the preferential excitation of guanine and its decomposition in quadruplex DNA by UVB-irradiation.

The substitution of 2-aminopurine (Ap) for A7 in the human telomeric sequence d[AGGG(TTAGGG)(3)] resulted in a significant increase in the fluorescence intensity of Ap for the conformational change from duplex to quadruplex.

Rapid cleavage of the naphthylmethyl-oxygen bond of 1- and 2-[(4-benzoylphenoxy)methyl]naphthalenes in higher triplet excited states occurred within a laser flash of 5 ns to give 1- and 2-naphthylmethyl radicals with formation quantum yields of 0.042 +/- 0.004 and 0.020 +/- 0.002, respectively, during two-colour two-laser flash photolysis.