Quantum cutting is an attractive optical phenomenon that one high-energy photon can be converted into two low-energy photons with photoluminescence quantum yields (PLQYs) above 100%. In this review, we introduce a novel approach to enhance the quantum cutting energy transfer in lanthanide ions as near-infrared (NIR) emitter by using all inorganic perovskite (CsPbCl₃) as the energy donor. Recently, the efficient quantum cutting phenomenon in Yb³⁺-doped CsPb(Cl,Br)₃ nanocrystals have been reported, which yields a photoluminescence quantum yield close to 200%. Such materials are expected to have applications in photoenergy converter for solar cells and NIR emitter for LEDs. Here, the material design (including film-type QC perovskites), optical properties and potential optoelectronic applications of lanthanide-doped metal halide perovskite nanocrystals are presented.

In this review, we describe a promising method for integrating functional chromophores into DNA structures to develop DNA-based photofunctional materials. This integration facilitates new approaches in the design of fluorescent probes and manipulation of photoinduced electron-transfer mechanisms, and enables the development of advanced materials that exploit the unique properties of DNA. Synthesis of chromophore-modified DNA will not only enhance our understanding of biomolecular interactions under light irradiation, but also enable the creation of light-responsive devices and materials. It highlights the potential of DNA-based technologies to develop the fields of phototherapy, environmental sensing, and energy conversion. This integration of DNA synthesis with supramolecular chemistry and nanotechnology will enable biological molecules to develop versatile photonic materials.

Photochemistry of indigo dyes is introduced in this review. The indigo chromophore is constituted from two pairs of adjacent NH and C=O groups with two intramolecular hydrogen bonds between them. Indigo itself is a stable pigment and does not exhibit photoisomerization because of the short excited state lifetime which is considered to be due to a nonradiative decay that occurs via intramolecular proton transfer. In fact, solvent-assisted photo-induced proton transfer was observed for indigo carmine in aqueous solution but not in other solvents. Indigo derivatives without intramolecular hydrogen bonds exhibit trans-cis photoisomerization. We have measured femtosecond transient absorption spectra of indigo derivatives, and found that those with absorption bands at shorter wavelengths have slow isomerization rates, while those at longer wavelengths have faster ones. The excited state lifetime of cis isomer is shorter than that of the trans isomer, and the quantum yield of cis → trans is larger than that of trans → cis photoisomerization.

It is important to develop the technology of production of green hydrogen for realization of the carbon neutral society. In recent years, the artificial photosynthetic photocatalyst has gained much attention as a promising production method of row-cost green hydrogen. In this topic, we introduce the stage-of-the-art single particulate metal oxide photocatalyst as artificial photosynthesis developed by our group. SrTiO₃ photocatalysts doped with aluminum and small amounts of transition metals such as Cr, Ir, Rh, and Ru show the high activity for water splitting under visible light irradiation. In addition, a Sr-doped NaTaO₃ photocatalyst loaded with a Rh-Ru dual metal cocatalyst evolve methane of an eight-electron reduction product by CO₂ reduction under UV light irradiation using water as an electron donor. Improvement in the quality of the host material and the development of the suitable cocatalyst as an active site are important issues for enhancement of the photocatalytic activity.

Beautiful fluorescence is very attractive in chemistry. For further applications of fluorescence, it is much important to control and modulate fluorescence color. So far, various techniques and methodologies have been proposed and demonstrated to control and modulate fluorescence color. All these approaches require touching the fluorescent material; modification of molecular structure, exchanging solvents (solvatochromism), and applying mechanical stress. In contrast, by using optical tweezers, we propose novel techniques that enable us to control and modulate fluorescence color in a remote and non-contact manner. We demonstrate that optical tweezers can control initial photochemical processes such as solvation, excimer formation, and FRET.

Trivalent lanthanide complexes are attractive candidates for light sources due to their exceptionally pure color emission. Enhancing the photoluminescence intensity through sensitization using ligands with high absorption efficiency is a powerful strategy. However, the microscopic energy transfer mechanisms from organic chromophores to lanthanide ions remain elusive. In this study, we investigated the energy transfer processes in luminescent trivalent europium (Eu³⁺) complexes using time-resolved photoluminescence spectroscopy and transient absorption spectroscopy. Our results successfully elucidated the energy transfer processes from two different ligands, revealing that both energy transfers occur via the triplet excited states of each ligand. Based on these findings, we proposed efficient sensitization using host-to-guest energy transfer in a host-guest film composed of aromatic organic molecules and Eu³⁺ complexes. Our approach resulted in a more than 400-fold enhancement of photoluminescence intensity compared to the intrinsic Eu³⁺ complex.

Photochemistry begins with light absorption by molecules and nanomaterials like semiconductor quantum dots and plasmonic metal nanoparticles, leading to electronic excitation or promotion of electrons to higher energy levels. The electronic excitation follows a series of photophysical and photochemical processes, such as energy transfer, electron transfer, and chemical reactions, which play crucial roles in multidisciplinary science by bridging the gap between various fields and facilitating interdisciplinary research collaborations. Its impact extends across diverse domains, including chemistry, physics, biology, materials science, environmental science, medicine, and engineering. Therefore, photochemistry is a central science that bridges the gap between different disciplines and nurtures researchers and programs in basic science and emergent technologies. Indeed, photochemistry society meetings play a crucial role as primary platforms for facilitating the exchange of ideas, fostering national and international academic interactions, and promoting research collaborations. These societies are catalysts for attracting young talents to physical sciences, interdisciplinary sciences, and technologies. Recent photochemistry society meetings, including the 2022 IUPAC Symposium on Photochemistry (28^th PhotoIUPAC), the 2023 International Conference on Photochemistry (ICP2023), the 2023 Annual Meeting of the Japanese Photochemistry Association (JPA), the 2023 Asian Photochemistry Conference (12^th APC), and the 2024 Inter-American Photochemistry Association (I-APS), serve as pivotal platforms for fostering international academic networks and advancing multidisciplinary science. This article delves into the contributions of these conferences, with a particular focus on the ICP, JPA, and APC meetings. Additionally, it provides insights into my experiences with the JPA, offering guidance to foreign newcomers navigating the Japanese academic landscape.