Atsushi Kobayashi

Photoinduced charge separation is crucial for converting solar energy to electrical and chemical energy. In this work, to improve the photoinduced charge separation efficiency at the photosensitizing dye–semiconductor interface, we synthesized two dual-porphyrin-sensitized Pt-loaded TiO2 nanoparticle photocatalysts (ZnP–Zr–SnP@Pt–TiO2 (DPSP) and SnP–Zr–ZnP@Pt–TiO2 (DPSP-r)) by reversing the loading order of two metalloporphyrin-photosensitizing dyes (SnP and ZnP = 5,10,15,20-tetrakis(p-carboxyphenyl)-porphyrinato-M; M = SnIVCl2, ZnII). The apparent quantum yield of the photocatalytic H2 production reaction over DPSP in a 500 mM l-ascorbic acid sacrificial electron donor aqueous solution (2.08%) was estimated to be approximately 10 times higher than that over DPSP-r (0.21%), indicating the importance of the loading order of the metalloporphyrin dye for efficient photoinduced charge separation. The barely emissive nature of the DPSP compounds and the redox potentials of ZnP and SnP suggested that the redox cascade structure of the dual-metalloporphyrin ZnP–Zr–SnP layer on the Pt–TiO2 nanoparticle surface plays a key role in photoinduced charge separation for photocatalytic H2 production. The combination of this dual-metalloporphyrin sensitization method and the versatility of the metalloporphyrin family promotes the development of highly active visible-light-driven photocatalysts.

Solar‐light‐driven photocatalytic coproduction of hydrogen (H ₂ ) and valuable organic compounds is a promising technique for realizing sustainable carbon neutral society. In this work, we fabricate a new dual‐product photocatalytic system for the coproduction of H ₂ and acetaldehyde/acetone by combining a dual Ru (II) dye‐sensitized Pt‐cocatalyst‐loaded TiO ₂ nanoparticles photocatalyst with a Pd(II)‐acetate/9‐azanoradamantane N‐oxyl (nor‐AZADO ^• ) double‐mediatory Wacker oxidation catalytic system. This photoredox cascade catalytic system successfully converts gaseous ethylene/propylene substrates into H ₂ and acetaldehyde/acetone under blue‐light irradiation owing to the electron mediation of nor‐AZADO ^• between the two (photo)catalytic cycles. The maximum turnover number per one photosensitizer and apparent quantum yield for the initial 1 h of irradiation in the presence of 5.0 vol% ethylene gas are estimated to be 1533 and 1.23%, respectively. These findings open a new avenue for simultaneously supplying clean energy resources, H ₂ and organic valuables via oxidative organic transformations.

H₂ evolving photodissolution of cellulose paper was successfully achieved by combining dual-dye-sensitized photocatalysts and a 2,2,6,6-tetramethylpiperidine 1-oxyl oxidation catalyst.

Visible‐light‐driven photocatalytic hydrogen (H₂) production has been extensively studied as a clean and sustainable energy resource. Although sacrificial electron donors (SEDs) are commonly used to evaluate photocatalytic activity, their irreversible decomposition forces charge separation, which disrupts the inherent dual productivity of photocatalysis, that is, the formation of both the reduction and oxidation products. To achieve highly efficient photoinduced charge separation without SED decomposition, the layer‐by‐layer assembly of redox‐active photosensitizing dyes and electron mediators through Zr⁴⁺‐phosphonate bonds has been extensively studied as an artificial mimic of the electron transport chain in natural photosynthesis. This concept paper presents an overview of photoredox cascade catalytic (PRCC) systems comprising multiple Ru(II)‐trisbipyridine‐type dyes and mediator layers on Pt‐loaded TiO₂ nanoparticles for H₂ production from redox reversible electron donors (RREDs). The PRCC structure‐activity relationship for photocatalytic H₂ production is briefly discussed in terms of layer thickness, surface structure and modification, and cooperativity with molecular oxidation catalysts. Finally, new insights into the design of efficient dual‐production photocatalysts based on the PRCC structure are presented.

The emissions of isomorphous Pt( ii ) and Pd( ii ) one-dimensional chains exhibited distinct thermal responses, revealing the limiting factor for extending the excited-state delocalization across multiple molecules through metallophilic interactions.

In organic−inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π‐conjugated molecules remains challenging due to facile aggregation by their strong π‐π interaction. In this report, a π‐conjugated scaffold insulated by covalently linked permethylated α‐cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier‐transformed infrared (FT‐IR) spectroscopy and X‐ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl‐terminated molecules, as confirmed by FT‐IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O ₂ reduction to H ₂ O ₂ with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H ₂ generation with iridium(III) dye‐sensitized Pt‐loaded TiO ₂ nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well‐defined hybrid interfaces.

A photoredox cascade catalyst for concurrent organic synthesis and hydrogen production was developed by combining a dual-dye sensitized Pt-TiO₂ photocatalyst and an N-hydroxyphthalimide hydrogen atom transfer catalyst.

The selectivity of the porous crystal phase of luminescent platinum(ii) complexes with Pt⋯Pt interactions has been systematically controlled by the ancillary N-heteroaryl carboxylate ligand.