Fluorescence enhancement of benzimidazolium derivative on clay nanosheets by surface-fixation induced emission (S-FIE).

The photophysical behaviors of benzimidazolium derivative [4-(1,3-dimethylbenzimidazol-3-imu-2-yl)-N, N-diphenylaniline (2-(4-(diphenylamino)phenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium)] (BID) in water, organic solvents and on synthetic saponite were investigated. The fluorescence quantum yield (Φf) of BID was 0.91 on the saponite surface under the optimal condition, while that in water was 0.010. Such fluorescence enhancement on the inorganic surface is called "surface-fixation induced emission (S-FIE)". This fluorescence enhancement ratio for BID is significantly high compared to that of conventional S-FIE active dyes. From the values of Φf and the excited lifetime, the non-radiative deactivation rate constant (knr) and radiative deactivation rate constant (kf) of BID on the saponite surface and in water were determined. Results showed that the factors for fluorescence enhancement were both the increase of kf and the decrease of knr on the saponite surface; especially, knr decreased by more than two orders due to the effect of nanosheets.

A Molecular Z-Scheme Artificial Photosynthetic System Under the Bias-Free Condition for CO2 Reduction Coupled with Two-electron Water Oxidation: Photocatalytic Production of CO/HCOOH and H2 O2.

Bio-inspired molecular-engineered systems have been extensively investigated for the half-reactions of H2 O oxidation or CO2 reduction with sacrificial electron donors/acceptors. However, there has yet to be reported a device for dye-sensitized molecular photoanodes coupled with molecular photocathodes in an aqueous solution without the use of sacrificial reagents. Herein, we will report the integration of SnIV - or AlIII -tetrapyridylporphyrin (SnTPyP or AlTPyP) decorated tin oxide particles (SnTPyP/SnO2 or AlTPyP/SnO2 ) photoanode with the dye-sensitized molecular photocathode on nickel oxide particles containing [Ru(diimine)3 ]2+ as the light-harvesting unit and [Ru(diimine)(CO)2 Cl2 ] as the catalyst unit covalently connected and fixed within poly-pyrrole layer (RuCAT-RuC2 -PolyPyr-PRu/NiO). The simultaneous irradiation of the two photoelectrodes with visible light resulted in H2 O2 on the anode and CO, HCOOH, and H2 on the cathode with high Faradaic efficiencies in purely aqueous conditions without any applied bias is the first example of artificial photosynthesis with only two-electron redox reactions.

Molecular Characteristics of Water-Insoluble Tin-Porphyrins for Designing the One-Photon-Induced Two-Electron Oxidation of Water in Artificial Photosynthesis.

Faced with the new stage of water oxidation by molecular catalysts (MCs) in artificial photosynthesis to overcome the bottle neck issue, the "Photon-flux density problem of sunlight," a two-electron oxidation process forming H2O2 in place of the conventional four-electron oxidation evolving O2 has attracted much attention. The molecular characteristics of tin(IV)-tetrapyridylporphyrin (SnTPyP), as one of the most promising MCs for the two-electron water oxidation, has been studied in detail. The protolytic equilibria among nine species of SnTPyP, with eight pKa values on the axial ligands' water molecules and peripheral pyridyl nitrogen atoms in both the ground and excited states, have been clarified through the measurements of UV-vis, fluorescence, 1H NMR, and dynamic fluorescence decay behaviour. The oxidation potentials in the Pourbaix diagram and spin densities by DFT calculation of the one-electron oxidized form of each nine species have predicted that the fully deprotonated species ([SnTPyP(O-)2]2-) and the singly deprotonated one ([SnTPyP(OH)(O-)]-) serve as the most favourable MCs for visible light-induced two-electron water oxidation when they are adsorbed on TiO2 for H2 formation or SnO2 for Z-scheme CO2 reduction in the molecular catalyst sensitized system of artificial photosynthesis.

A behavioural correlate of the synaptic eligibility trace in the nucleus accumbens.

Reward reinforces the association between a preceding sensorimotor event and its outcome. Reinforcement learning (RL) theory and recent brain slice studies explain the delayed reward action such that synaptic activities triggered by sensorimotor events leave a synaptic eligibility trace for 1 s. The trace produces a sensitive period for reward-related dopamine to induce synaptic plasticity in the nucleus accumbens (NAc). However, the contribution of the synaptic eligibility trace to behaviour remains unclear. Here we examined a reward-sensitive period to brief pure tones with an accurate measurement of an effective timing of water reward in head-fixed Pavlovian conditioning, which depended on the plasticity-related signaling in the NAc. We found that the reward-sensitive period was within 1 s after the pure tone presentation and optogenetically-induced presynaptic activities at the NAc, showing that the short reward-sensitive period was in conformity with the synaptic eligibility trace in the NAc. These findings support the application of the synaptic eligibility trace to construct biologically plausible RL models.

Factors for the emission enhancement of dimidium in specific media such as in DNA and on a clay surface.

Dimidium (3,8-diamino-5-methyl-6-phenylphenanthridinium: NH2PhP) is a well-known fluorophore as a DNA probe, although its fluorescence enhancement mechanism is not clear. In this study, we investigated the fluorescence enhancement mechanism of NH2PhP on a clay surface by observing the fluorescence behavior. Four systematically selected phenanthridinium derivatives (PDs): NH2PhP, 3,8-bisdimethylamino-5-methyl-6-phenylphenanthridinium (NMe2PhP), 5-methyl-6-phenylphenanthridinium (PhP) and 5-methylphenanthridinium (P) and synthetic clay were used as guest and host materials, respectively. It was revealed that the suppression of hydrogen bonding with water (N-HOH or NH-OH2) is the dominant factor for the fluorescence enhancement on the clay surface for NH2PhP and NMe2PhP. In addition, judging from the fluorescence enhancement for NH2PhP, NMe2PhP and PhP and no fluorescence enhancement for P on the clay surface, the suppression of rotation of the phenyl ring was indicated to make a partial contribution to the fluorescence enhancement mechanism. Because the fluorescence enhancement behavior was quite similar on the clay surface and in DNA, the obtained results afford an important clue to discuss the fluorescence enhancement mechanism of NH2PhP in DNA.