Tetsuo Yamaguchi

Lead halide perovskite nanocrystals (PNCs) are promising energy donors for organic dyes, yet the factors determining whether Förster resonance energy transfer (FRET) or Dexter‐type electron‐exchange transfer (DET) dominates remain unclear. Here, we investigate energy transfer (ET) mechanisms in CsPbBr ₃ PNC–Cy3 linkages as a function of PNC size using ensemble spectroscopy and single‐PNC measurements. In small PNC–Cy3 linkages, the experimentally determined ET efficiencies from PL quenching and lifetime shortening agree well with theoretical FRET efficiencies, and the donor decay time matches the acceptor rise time, identifying FRET as the dominant pathway. In contrast, large PNC–Cy3 linkages exhibit ET efficiencies exceeding theoretical FRET values and a faster donor decay than the acceptor rise, with both dynamics much faster than expected for FRET, supporting the involvement of a stepwise DET pathway. PLQY analysis further indicates that a nonemissive quenching pathway competes with ET to Cy3 and supports a model in which stepwise DET is initiated by hole transfer from the PNC to Cy3, followed by electron transfer. Single‐PNC measurements corroborate the ensemble results. These findings reveal that PNC size controls the competition between FRET and DET by modulating the donor–acceptor distance, providing a design principle for selectively controlling ET pathways in PNC–dye assemblies.

The emission photon statistics and blinking dynamics of lead halide perovskite nanocrystals (PNCs) are strongly influenced by quantum confinement, Auger recombination (AR), and carrier trapping, yet their direct correlation with nanocrystal size remains unresolved. Here, we correlate size and optical properties of individual CsPbI₃ PNCs by combining single-particle spectroscopy with atomic force microscopy. PNCs smaller than ∼12 nm exhibit pronounced quantum confinement, strong photon antibunching with g⁽²⁾(0) ≤ 0.2, and band-edge carrier blinking. As the size increases, the photoluminescence red shift weakens and g⁽²⁾(0) increases, approaching unity above ∼17 nm. Femtosecond transient absorption measurements reveal strongly suppresses AR in larger PNCs, while the dominant blinking mechanism shifts from the band-edge carrier to Auger blinking at ∼16–18 nm. These results establish design principles for stable quantum light emitters and size-tunable optoelectronic materials.

Colloidal semiconductor quantum dots (QDs) can generate multiple excitons (MXs) within a single QD. Owing to their large absorption cross-section, efficient utilization of MX is anticipated for the development of light-harvesting systems. However, MXs typically undergo nonradiative decay via Auger recombination (AR). In this study, we investigated the possibility of energy transfer from the MXs in a single QD to multiple cyanine dyes (Cy3) adsorbed on the QD surface. Based on the linear relationship between the AR lifetime and QD volume, formamidinium lead bromide perovskite nanocrystals (PNCs) with three distinct size distributions were synthesized. Simultaneous measurements of emission photon correlations and individual pristine PNC sizes revealed that the probability of multiphoton emission increased in PNCs larger than 12 nm. This was attributed to a slowdown in the AR rate, which was evaluated by transient absorption spectroscopy. Subsequently, multiple Cy3 dyes were adsorbed onto the PNCs as energy acceptors to evaluate the transfer of energy from the MXs to multiple Cy3 dyes. Photon correlation measurements of Cy3 emission via energy transfer─induced by excitation of a single PNC─showed an increased probability of multiphoton emission in PNC-Cy3 systems with PNC sizes exceeding 12 nm. These findings indicate that multiple Cy3 dyes were excited and emitted via the energy transfer from MXs. Thus, we clearly demonstrate that energy transfer from MXs to multiple surface dyes is feasible using large-sized PNCs.

The surface morphology of Mg-Al-layered double hydroxide (LDH) was successfully controlled by reconstruction during systematic phase transformation from calcined LDH, which is referred to as layered double oxide (LDO). The LDH reconstructed its original phase by the hydration of LDO with expanded basal spacing when reacted with water, including carbonate or methyl orange molecules. During the reaction, the degree of crystal growth along the ab-plane and stacking along the c-axis was significantly influenced by the molecular size and the reaction conditions. The lower concentration of carbonate gave smaller particles on the surface of larger LDO (2000 nm), while the higher concentration induced a sand-rose structure. The reconstruction of smaller-sized LDH (350 nm) did not depend on the concentration of carbonate due to effective adsorption, and it gave a sand-rose structure and exfoliated the LDH layers. The higher the concentration of methyl orange and the longer the reaction time applied, the rougher the surface was obtained with a certain threshold point of the methyl orange concentration. The surface roughness generally increased with the loading mount of methyl orange. However, the degree of the surface roughness even increased after the methyl orange loading reached equilibrium. The result suggested that the surface roughening was mediated by not only the incorporation of guest molecules into the LDH but also a crystal arrangement after a sufficient amount of methyl orange was accommodated.

Release of ferulic acid from surface-functionalized hollow nanoporous silica particles (HNSPs) was investigated in deionized water (DI water) and in ethanol. The host material, an HNSP, was synthesized in the presence of polymer and surfactant templates, and the pore as well as the surface were modified with either pentyltriethoxysilane (PTS) or octyltriethoxysilane (OTS) through silane coupling reactions. The inner hollow space occupied a volume of ~45% of the whole HNSP with a 2.54 nm pore channel in the wall. The pore size was estimated to decrease to 1.5 nm and 0.5 nm via the PTS and OTS functionalization, respectively. The encapsulation efficiencies of the HNSP (25 wt%), PTS-functionalized HNSP (PTS-HNSP, 22 wt%) and OTS-functionalized HNSP (OST-HNSP, 25 wt%) toward ferulic acid were similar, while the %release in DI water and ethanol varied following HNSP > PTS-HNSP > OTS-HNSP. Release kinetic analyses with Korsmeyer–Peppas fitting suggested a trade-off relationship between the solvent’s ability to access the HNSP and the affinity of ferulic acid to the surface, allowing us to understand the solvent’s controlled release rate and mechanism.

Pioneered by the success on active transport of ions across membranes in 1980’ using the regulation of the binding properties of crown ethers with covalently linked photoisomerizable units, extensive studies on the movements by using varied interactions between moving objects and environments have been reported. Photoinduced movements of various objects ranging from molecules, polymers to microscopic particles were discussed from the aspects of the driving for the movements, materials design to achieve the movements and systems design to see and to utilize the movements are summarized in this review. Grafical Abstract

Interactions between layered double hydroxide (LDH) nanomaterials and plasma proteins according to their particle size and surface charge were evaluated. The LDHs with different particle size (150, 350 and 2000 nm) were prepared by adjusting hydrothermal treatment and urea hydrolysis and subsequent organic coating with citrate, malite and serite was applied to control the surface charge (ζ-potential: −15, 6 and 36 mV). Adsorption isotherms and Stern–Volmer plots for fluorescence quenching indicated that the human blood plasma had weak interactions toward all the types of LDHs. The adsorption isotherms did not show significant differences in the size and surface charges, while the fluorescence quenching ratio increased with the increase in the surface charge, implying that electrostatic interaction played a major role in their interactions. The fluorescence quenching of three types of plasma proteins (human serum albumin, γ-globulin and fibrinogen) by the surface charge-controlled LDHs suggested that the proteins adsorbed on the LDHs with a single layer and additional proteins were weakly adsorbed to surround the LDHs with adsorbed proteins. It was concluded that the LDH nanomaterials are fairly compatible for blood components due to the protein corona while the electrostatic interaction can affect their interaction with the proteins.

Gentamicin was stabilized in a bentonite clay via periodic charge–charge interaction and was successfully incorporated into a polymer film for long-term sustained antibacterial coating.

Efficient negative photochromism was achieved by the photoinduced migration of merocyanine in mesoporous silica to an organophilic clay as spiropyran. Depending on the nature of the organophilic clays (dioctadecyldimethylammonium and dioleyldimethylammonium clays), important differences in the negative photochromisms and the thermal coloration were observed; the dioleyldimethylammonium clay gave a higher yield (98%) and faster reaction (half-life t_1/2 = 2.8 h) than the dioctadecyldimethylammonium clay (94% and t_1/2 = 3.2 h) of the negative photochromism, indicating the important role of the surfactant assembly to control the molecular diffusion.