Caged compounds, which temporally inactivate bioactive compounds using photo-labile protecting groups (PPGs), are physiologically useful, because the bioactive compounds may be spatiotemporally released (=uncaged) upon photolysis to investigate the mechanism of bioactivity in living tissues. Highly efficient uncaging and appropriate water solubility are the crucial factors for the practical use in vivo studies. In addition to the fundamental factors, the near IR (NIR) excitation of caged molecules using 650-1050 nm renders deeper investigation of the role of bioactive substances, because the light can reach the deeper site of tissues. The two-photon (TP) excitation technique using NIR light realizes a highly spatiotemporal control of the release of bioactive molecules. In this review, the strategy to design TP-responsive molecules and recent developments of PPGs with TP absorption character are summarized.

Polymer solar cells based on a donor conjugated polymer and an acceptor fullerene derivative have recently attracted much attention as a next generation solar cell. The photovoltaic conversion processes include photon absorption, exciton diffusion to a donor/acceptor interface, charge transfer at the interface, charge dissociation into free charge carriers, and charge collection to each electrode, which are ranging from 10⁻¹⁵ to 10⁻⁶ s on a time scale. Thus, time-resolved spectroscopic techniques such as transient absorption measurements are one of the most powerful tools for observing these photovoltaic conversion processes directly. In this review, we overview recent progress in spectroscopic studies on photovoltaic conversion mechanism in polymer solar cells. First, we describe exciton diffusion dynamics in crystalline polymer domains studied by analyzing singlet–singlet exciton annihilation. Next, we discuss how polymer crystallinity impacts on charge generation dynamics in polymer solar cells. Finally, we describe bimolecular charge recombination dynamics in polymer solar cells studied by transient absorption and transient optoelectronic measurement techniques.

Conjugated polymer nanoparticles (Pdots) have recently emerged as a new class of fluorescent nanoparticles. Their application ranges from fluorescent probes and sensors to photocatalysis and phototherapy. All these applications are based on the knowledge obtained from basic researches on their (photo)chemical and (photo)physical properties. In this review article, I first introduce fundamental researches that serve as a foundation of the applications of Pdots, in particular molecular designs of conjugated polymers (CPs) that define underlying properties of Pdots, size control of Pdots that is required in many applications including the fabrication of ultrasmall particles, and the regulation of CP-chains interactions inside Pdots that have a significant effect on photophysical properties of Pdots. On that basis, I also discuss applications of Pdots and their future outlook.

Room temperature phosphorescence of metal-free organic crystals has been vigorously reported in recent years. Due to their applicability in many fields as a bio-imaging probe, oxygen sensor, or OLED, these compounds have attracted much attention. The phosphorescence emission by photoexcitation requires a preceding intersystem crossing, a forbidden spin flip of an electron. Hence, the mechanism of the forbidden process is a center of attention. In this review, we introduce recent findings of heavy-atom-free, crystalline organic compounds with room temperature phosphorescence property, focusing on their intersystem crossing mechanisms.

The unique properties of layered double hydroxides (LDH) availed with the photocatalytic conversion of CO₂ into CO in water. Ga₂O₃ photocatalysts modified with Mg−Al LDH, which concentrate CO₂ molecules near Ag cocatalysts, enhanced not only the amount of CO evolved but also the selectivity toward CO evolution. The composite photocatalysts between Ga₂O₃ and Mg−Al LDH are crucial for the selective reduction of CO₂ to CO in water, though Mg−Al LDH itself does not work as a photocatalyst. On the other hand, the presence of chloride ion (Cl⁻) in the reaction solution brought the photocatalytic activity on the LDHs themselves. The stoichiometric formation of hypochlorous acid (HClO) as an oxidation product of Cl⁻ was accompanied by the high evolution of CO as a reduction product of CO₂.

Photosynthetic light-harvesting antenna proteins play important roles in efficient solar energy conversion in natural photosynthetic systems. The arrangement of photofunctional pigments in photosynthetic antenna proteins is the basis of efficient light-harvesting abilities of these proteins. Utilization of such pigment arrangement will be useful to develop artificial photofunctional nano-biomaterials. From this viewpoint, we focus on functionalization of peripheral light-harvesting proteins (LH2) in purple photosynthetic bacteria by pigment removal. We have successfully prepared LH2 proteins that lack energy-donating B800 bacteriochlorophyll (BChl) a and inserted chlorophyll (Chl) derivatives into the cavity of the B800 binding sites. Production of regularly arranged nano-spaces in photosynthetic proteins by pigment removal will be a novel strategy to functionalize photosynthetic proteins and to develop porous protein materials.

We demonstrate that a statistically-significant chiral bias can be observed in NaClO₃ chiral crystallization induced by circularly polarized laser trapping of Ag nano-aggregates at the air/an unsaturated solution. A continuous-wave visible laser (λ = 532 nm) was used as the light source. The "dominant" enantiomorph was switchable by changing the handedness of the circularly polarized laser, indicating that the chiral bias is enantioselective. The resulting crystal enantiomeric excess (CEE) reached approximately 25%. The CEE is much higher than the typical enantiomeric excess (ee) in asymmetric photosynthesis of organic compounds ranging from 0.5 to 2%. The efficient chiral bias may be due to the plasmon-induced circular dichroism by coupling between chiral pre-nucleation crystalline cluster and localized surface plasmon of the Ag nanoparticles. Our results shed a light not only to the mechanism of chiral nucleation but also to evaluation method for ee of chiral compounds synthesized in chiral plasmonic near-field.

The mechanism for a polymerization under UV light exposure without using initiators in liquid crystals (LCs) was investigated in this study. Experimental results of IR spectroscopy, high performance liquid chromatography, SEM, and TEM revealed that the polymerization of the monomer 2,6-dimethacryloyl-oxy-naphthalene (2,6-DMANaph) was presumed to be occurred with generation of radicals from the monomer as reactive intermediates of photo-Fries rearrangement. As the initiators are not needed when polymer layers are formed in LC cells with the monomer 2,6-DMANaph, voltage holding ratio is kept high.