Excited-state intramolecular proton transfer (ESIPT) is a fascinating and unique photoisomerization process, resulting in characteristic emission properties. This review highlights recent advances in excited-state switching in ESIPT-type compounds and their emission behaviors. Precise and appropriate molecular design provides us a variety of emissive excited states possessing keto, enol and other geometries. We, furthermore, summarize multi-state fluorescence behavior on ESIPT-type compounds in terms of solvent, hydrogen bond and acid–base reaction. These findings render the essential role of excited-state electronic structures in governing photophysical behaviors toward a unified design strategy for functional luminescent materials.

Organic molecules rarely exhibit phosphorescence at room temperature because spin-forbidden emission from the triplet state is intrinsically slow and is easily outcompeted by nonradiative decay and oxygen quenching. In crystals, however, restricted molecular motions, well-defined intermolecular interactions, and solid-state barriers to oxygen diffusion can dramatically prolong triplet lifetimes and enhance emission, making room-temperature phosphorescence (RTP) a designable function. This review summarizes crystal-engineering design principles for RTP in purely organic crystals by integrating three key requirements: (i) efficient triplet formation, (ii) triplet stabilization, and (iii) radiative triplet emission. We discuss strategic levers such as tuning molecular packing and polymorphism, exploiting co-crystallization and host–guest architectures to create rigid environments, introducing external heavy-atom or local-field effects without covalent modification, and engineering defect/trap states and oxygen-shielding pathways.

Lead halide perovskites have attracted much attention as semiconductor materials for applications in solar cells, light-emitting diodes, and photodetectors due to their facile synthesis, high photoluminescence (PL) quantum yields, and size- and halide-dependent tunable optical bandgaps. Recently, highly ordered assemblies of perovskite nanocrystals (PNCs), known as supercrystals, as well as ligand-stripped PNC assemblies have emerged as a topic of growing interest due to their unique optical properties, which differ from those of isolated PNCs or randomly aggregated PNC films. However, the correlation between the structural characteristics of such PNC assemblies and their PL properties remains unclear. It is crucial to gain a systematic understanding of the relationship between PNC alignment and exciton/carrier recombination dynamics in the PNC assemblies. This review introduces research on the control of PL properties in perovskite microcrystals and PNC films, as well as assembly structure and PL control of perovskite quantum dot assemblies and supercrystals.

Establishing artificial photosynthesis is a key challenge for a sustainable energy society. This review focuses on the photochemical hydrogen evolution from water catalyzed by cobalt complexes bearing N-heterocyclic carbene ligands (Co-NHC1, 2). Unlike traditional cobalt catalysts, Co-NHC1, 2 exhibit unique catalytic activity even under extremely low driving force conditions (ca. 150 meV) in a system consisting of [Ru(bpy)₃]²⁺ and methylviologen (MV²⁺). We discuss strategies to enhance the catalytic performance, including the redox tuning of viologen-based electron relays and the elimination of nitrate anions, which are identified as radical scavengers that inhibit the reaction. Furthermore, detailed mechanistic studies combined with DFT calculations reveal that the reaction proceeds via a unique concerted proton-electron transfer (CPET) mechanism. The catalytic cycle involves a “double CPET” pathway, analogous to the Volmer-Heyrovsky mechanism on metal electrodes, allowing the catalysts to bypass the thermodynamically unfavorable Co(I) intermediate.

Optical vortices possess a helical wavefront and donut-shaped intensity distribution and carry orbital angular momentum (OAM) characterized by a topological charge. When the OAM is transferred to materials, it acts as a torque that induces rotation and twisting. In this study, cylindrical microstructures reflecting the intensity distribution of an optical vortex were fabricated via two-photon polymerization of a UV-curable resin using a femtosecond optical vortex laser. The diameter and height of the structures were dependent on the laser intensity. A helical periodic structure with a width below the diffraction limit was observed on the inner surface of the cylinder. The handedness of the helical periodic structure corresponded to the sign of the topological charge. These results suggest that the OAM of the optical vortex plays a role in the formation of helical periodic structures.

Organic luminescent radicals have attracted increasing attention because of their unique doublet emission mechanism. This article summarizes recent progress in carbazole-substituted tris(2,4,6-trichlorophenyl)methyl (TTM) radicals, focusing on strategies to improve photostability and to control emission wavelength. In particular, we discuss how donor substitution and dendritic structures influence excited-state character and photophysical properties. By introducing a model that incorporates electron–electron repulsion effects, we provide a conceptual explanation for unexpected spectral shifts observed upon increasing the number of carbazole units. The relationship between electronic structure, stability, and emission efficiency is highlighted to offer design guidelines for next-generation radical-based luminophores. Furthermore, the potential of water-soluble luminescent radicals for dual fluorescence and magnetic resonance imaging is briefly discussed.