The time-dependent density functional (TD-DFT) method, a method for calculating excited states based on density functional theory (DFT), is often used as a convenient way to calculate photoelectron absorption spectra. However, there are often the cases where experiments and calculations do not correspond, and a prescription for this issue is required. In this review, a practical example of model chemistry for the calculation of absorption spectra using TD-DFT is presented. The target molecule of the calculation is a diarylethene derivative that undergoes a photochromic reaction, and the tuning of the calculation method (here, the parameters of the exchange-correlation functional) with and without experimental values (spectra) of the basic parental molecule is described. We found that the parameter tuning both with and without experimental data give almost identical results, which well reproduce the experimental spectra.

The effect of diffusion on photoexcited carrier kinetics has been studied for decades. However, many difficult issues remain unresolved. For example, when the concentration of photoexcited carriers is high, diffusive mixing of photoexcited carriers proceeds with time. Immediately after pulsed excitation, the photoexcited carriers are expected to interact with their nearest neighbour carriers, and as time passes, diffusive mixing proceeds and free carriers are generated. The delayed fluorescence due to triplet-triplet annihilation (TTA) in organic solids are reviewed, followed by recent results on diffusive mixing. We also present recent results on bulk reactions of electrons and holes in particulate photocatalysts. The bulk reactions of carriers in semiconductors are well studied by using the semiconductor equations. However, for particulate photocatalysts, boundary conditions at the interface with water need to be considered. The quantum yield of photocatalysts under solar irradiation is discussed.

This review is concerned with metal complex catalysts, which are well documented as CO₂ reducing photocatalysts. In order for a metal complex catalyst to function as a photocatalyst in isolation, it must possess two essential characteristics. The first is the capacity to reduce CO₂; the second is the ability to form a stable excited state, which enables the utilization of absorbed light energy in the reaction. In recent years, research has focused on the development of systems that utilize separate complexes for catalytic and photosensitization reactions. Nevertheless, there have been reports of enhancements in catalytic efficacy even with metal complex catalysts alone. In this review, we will present a synthesis of past and recent reports on the extent of the improvements in performance using mononuclear metal complex photocatalysts.

The author designed an organic-inorganic hybrid photocatalyst for production of hydrogen peroxide (H₂O₂) by using water as an electron source. The organic-inorganic hybrid photocatalyst was prepared by immobilizing diprotonated dodecaphenylporphyrin (H₄DPP²⁺) derivatives as a selective reduction catalyst of O₂ having carboxyl groups to be anchored to the surface of TiO₂ as an oxidation photocatalyst of water. The H₄DPP²⁺-TiO₂ hybrid photocatalyst dispersed in pure water was irradiated at 365 nm LED lamp under air. Formation of H₂O₂ was confirmed by iodometry of the supernatant and the amount of H₂O₂ was determined to be 0.3 mM for 1 min photoirradiation. Thus, the H₄DPP²⁺-TiO₂ hybrid photocatalyst performs water oxidation at the TiO₂ surface and selective two-electron reduction of O₂ at the H₄DPP²⁺ moiety, respectively.

A comprehensive understanding of the transmission of nanoscale forces in the pico-to-nanonewton range is essential in the field of polymer physics. While physical approaches have limitations in analyzing the local force distribution in condensed environments, chemical analysis using probes represents a promising avenue. In this topic, we will outline recent advances in the development of ratiometric fluorescent force probes and newly obtained insights into polymer physics. After an overview of the photophysical properties of the force probes, the following studies will be presented: 1) quantitative evaluation of local stress concentration in crosslinked polyurethane elastomer, 2) development of a force probe that works in polymer gels, and 3) simultaneous monitoring of polymer chain stretching and subsequent strain-induced crystallization. The combinational use of the dual-emissive force probe and the ratiometric fluorescence imaging is a universal approach for the development of soft matter physics.

Highly luminescent compounds with high color purity are becoming increasingly important in the development of display and sensing materials. Among the various luminophores, trivalent lanthanide (Ln(III)) complexes (especially Eu(III) and Tb(III) complexes) are promising candidates for achieving pure color luminescence owing to their 4f–4f transition. The brightness of Ln(III) emission is determined by the product of the light-absorption coefficient of organic ligands and the emission quantum yield due to the excitation of organic ligands. Thus, controlling the electronic structure of ligands is crucial for developing luminescent Ln(III) complexes with high brightness. Herein, a design strategy based on the triplet-state control of ligands toward the development of highly luminescent Ln(III) complexes is demonstrated.