Since the first synthesis of [2.2]paracyclophanes in 1949, a wide variety of the derivatives have been synthesized, and their physical properties have been extensively investigated. However, there have not been many cases in which [2.2]paracyclophanes have been applied beyond the field of organic chemistry and organometallic chemistry. In the first half of this paper, the through-space conjugation and photoluminescence properties of π-stacked molecules (polymers and oligomers) consisting of [2.2]paracyclophane as a key unit are introduced. One of the characteristics of the [2.2]paracyclophane skeleton is planar chirality without chiral center(s). Due to the suppressed rotational motion of benzene rings in [2.2]paracyclophane, it exhibits planar chirality depending on the substitution position(s). In the latter half, circularly polarized luminescence (CPL) profiles of some optically active π-stacked molecules based on the planar chiral [2.2]paracyclophane moiety are introduced.

Electrochemical polymerization is known as one of the methods for fabricating conductive polymer thin films. This method involves the electrolysis of a corresponding monomer solution with an electrolyte to form an insoluble conductive polymer thin film on the surface of an electrode. Functional molecule-conductive polymer composite thin films can also be obtained by electrochemical polymerization using a mixed solution of different monomers with the electrolyte. Additionally, multilayered conductive polymer thin films with different properties can be formed via sequential electrochemical polymerization, which is particularly useful for the fabrication of organic electronic devices. In this article, research on photoelectric conversion systems using electrochemically polymerized polythiophene will be summarized, with a focus on our previous work involving photoelectric conversion systems with electrochemically polymerized polythiophene films incorporating porphyrin and fullerene, as well as related research.

Artificial photosynthesis, which converts earth-abundant resources into fuels by sunlight, is a critical challenge for the development of sustainable energy society. H₂O₂ has received growing interest as a new liquid solar fuel because it is storable and transportable and generates electricity in a direct peroxide–peroxide fuel cell. Theoretically, H₂O₂ can be generated from earth-abundant water and O₂ by semiconductor photocatalysis under sunlight irradiation, via the oxidation of water by the valence band holes and two-electron reduction of O₂ by the conduction band electrons. However, early reported photocatalysts exhibited low efficiencies for H₂O₂ generation. Recent reports have revealed that some organic semiconductor photocatalysts generated H₂O₂ relatively efficiently under visible light. In this review, we outlined the recent advances in the catalyst design and photocatalytic solar H₂O₂ generation.

Organic electroluminescence (EL) devices have significantly advanced in recent years, becoming an essential technology in modern society. Recent research has focused on improving efficiency and developing new materials, with particular attention on thermally activated delayed fluorescence (TADF) and organic phosphorescent materials. Many functional compounds utilizing π-electron systems and main-group elements have been designed, with boron (a Lewis acid) and nitrogen (a Lewis base) playing crucial roles. This review highlights the recent developments in planar organic boron compounds, focusing on their fundamental photophysical properties, latest research findings, and applications in transition metal complexes. Planar organic boron compounds exhibit unique photophysical characteristics and contribute to the advancement of luminescent materials, particularly through their applications in metal complexes.

The development of typical element complexes, particularly those based on BODIPY and its derivatives, has recently become a key focus of research, primarily for applications in light-emitting devices, sensors, and photocatalysts. However, despite aluminum (Al) being in the same Group 13 as boron and its abundance and low cost, Al-based luminescent complexes have received surprisingly limited attention. This study introduces a novel class of functional dyes based on an aluminum-based dinuclear triple-stranded helicate, comprising three ligands and two aluminum ions. The complex, with its unique combination of rigidity and flexibility, enables intense luminescence and a large Stokes shift. Moreover, it exhibits circular dichroism (CD) and circularly polarized luminescence (CPL) properties arising from helical chirality. The creation of a mixed-ligand triple-stranded helicate also promotes efficient inter-ligand charge transfer (ILCT), facilitating the generation of excited triplet states. These distinctive properties highlighted its promising potential for diverse applications.

We have investigated the amplified photochemical reactions of aqueous organic nanocolloids induced by intense short-pulse laser excitation. When an intense 532-nm, 6-ns pulse laser was irradiated to the closed-ring isomer of the P-type diarylethene, the ring-opening reaction quantum yield increased nonlinearly to the excitation laser intensity, which was not observed in the solution phase. Also, the 355-nm, 6-ns laser irradiation to the T-type spironapththooxazine increased the reaction yield from the spiro form to the merocyanine form by three times or more than the CW 360-nm light for 1 second. These amplified photochromic reactions were discussed in terms of the laser heating and the sequential cooling of the nanoparticle in a single nanosecond laser pulse. A photo-synergetic interaction between multi-chromophore and multi-photon is indispensable for drastically enhancing the photochromic reaction in the nanocolloids.

Cyclometalated Ir(III) complexes are widely recognized as effective photosensitizers for diverse photochemical applications, including photocatalytic proton/CO₂ reduction and photoredox catalysis in synthetic organic chemistry. These complexes exhibit long-lived triplet excited states and tunable redox properties, achieved through strategic ligand design. In this study, we developed ionic Ir(III) complexes incorporating coumarin 6 as a cyclometalating ligand, which demonstrate strong visible-light absorption and function as efficient photosensitizers in visible light-driven H₂ generation reactions. However, the reactions usually require substantial amounts of organic solvents to solubilize the target Ir(III) photosensitizers. To address this unsustainable issue, a more environmentally benign H₂-generating system was constructed in an aqueous solution by embedding the Ir(III) complexes into lipid membranes. Additionally, a novel ion-pairing strategy was newly introduced to enhance the stability of Ir(III) photosensitizers during CO₂ photoreduction on lipid membrane surfaces.