Many organic molecules exhibit weak luminescence in the solid state due to aggregation-caused quenching, while exhibiting strong luminescence in solution. In contrast, aggregation-induced emission (AIE) is a phenomenon that enables strong luminescence in the solid state and has attracted much attention from the viewpoint of application in the solid-state emissive materials. Thus, it is essential to understand the AIE mechanism including the excited-state dynamics. In the early stages of advocating the AIE phenomenon, the quantum mechanical studies proposed the restriction of the intramolecular motion (RIM) model for the AIE mechanism. Recently, both quantum chemical calculations and time-resolved spectroscopies have suggested the contribution of the conical intersection (CI) and deduced the importance of restricted access to a conical intersection (RACI) model in the potential energy surface (PES). In this review, we introduce recent studies on the excited-state dynamics of AIE compounds and molecular design strategies guided by this understanding.

Semiconductor nanocrystals, also known as quantum dots (QD), can generate multiple excitons in a single QD. Thanks to their higher photostability and larger absorption cross-section compared to typical organic molecules, QDs are considered promising candidates for efficient light-harvesting materials. However, the multiple excitons generated in QDs interact with each other and annihilate through a process known as Auger recombination. As a result, the utilization of the multiple excitons is limited by Auger recombination. In this review, we introduce approaches to overcome the limitation, focusing on enhancing multiphoton emission from the multiple excitons by plasmonic effects and extracting multiple excitons through energy transfer to surface-bound organic molecules.

Chemosensors are analytical tools at the molecular level that allow visualization of chemical information through optical changes. Owing to their inherent cross-reactivities, chemosensors on an array enable multianalyte sensing based on pattern recognition. Polythiophene derivatives as chemosensors can be easily functionalized with molecular recognition moieties at the 3- and/or 4-position of thiophene rings. Upon analyte capture at side chains, various optical changes of polythiophene are induced by molecular wire effects and dynamic structural changes in the π-conjugated systems. The beneficial properties of polythiophene contribute to obtaining information-rich chemical information to discriminate analytes qualitatively and quantitatively in both solution and solid states. This short review summarizes the potential of amphipathic polythiophene derivatives for chemosensors and their arrays.

Optical control of molecular motion under ambient conditions remains a fundamental challenge, primarily due to thermal fluctuations, low molecular polarizability, and limited optical forces. To address these limitations, the exploitation of localized surface plasmon resonance, which generates highly enhanced electric fields, has emerged as a promising approach. Nevertheless, precise manipulation of small molecules at the few-nanometer scale remains technically demanding. In this report, we present our recent efforts to achieve molecular manipulation under ambient conditions through surface-enhanced Raman scattering observations. We systematically investigated the influence of solvents and electrolytes on molecular adsorption and diffusion dynamics. Furthermore, by applying electrochemical potential control, we realized selective molecular manipulation through charge-transfer resonance under defined potential. Our results demonstrate the feasibility of site-selective trapping and highlight the critical roles of molecular interactions and resonant excitation processes in light-induced molecular condensation. This work provides fundamental insights into nanoscale molecular control and offers new design principles for future photochemical applications.

Photochromic compounds, which can switch their color and properties by reversible photoisomerization, have been widely studied aiming for the application such as sensing, optical memory, or photo-switching materials. Among them, various diarylethenes have been developed as one of the most promising motifs due to their high fatigue durability and thermal stability. However, the effect of the distortion of the aromatic skeletons on photochromic behavior has not been clarified yet. Corannulene, a bowl-like curved aromatic compound, has attracted much interest focusing on their features such as a geometrical and electronic anisotropy and bowl-to-bowl inversion, which are different from those of typical planar aromatic compounds. Thus, photochromism of diarylethenes with corannulene is demonstrated to discuss the effect of curved aromatic skeletons on photochromism of diarylethenes.

We report on the terahertz electric field detection by the Stark effect as well as by the Pockels effect in electro-optic polymers. Both the Stark effect and the Pockels effect are one of the second-order nonlinear optical effects. The Stark effect is proportional to the product of imaginary part of the second-order nonlinear optical susceptibility Im χ⁽²⁾(-ω;ω,0) and the electric field E and related to the change in the extinction coefficient Δκ, while the Pockels effect is proportional to the product of real part of the second-order nonlinear optical susceptibility Re χ⁽²⁾(-ω;ω,0) and the electric field E and related to the change in the refractive index Δn. Thus, the Stark effect and the Pockels effect are the resonant second-order nonlinear optical effect and the non-resonant second-order nonlinear optical effect, respectively. We have developed new processing techniques such as a transfer technique of electro-optic (EO) polymers and a fabrication technique of free-standing and laminated films of EO polymers for the terahertz electric field detection. The advantages on the ultra-high frequency electric field detection by using EO polymers are also discussed from the viewpoint of the dielectric constant or refractive index at ultra-high frequencies and optical frequencies.