Artificial Photocatalytic System Using Polydiacetylene-(-NH-phen)Ru(bpy)₂ for Cofactor Regeneration and CO₂ Reduction

(Chemical Equation Presented) For the practical use of a photobioreactor for artificial photosynthesis, efficient visible light-absorbing materials have to link reduction and oxidation catalysts for an efficient energy flow. As a step toward this goal of an NADH regeneration system and enzymatic production of solar fuels from CO₂, we report the synthesis of a new polydiacetylene compound that is covalently connected with [Ru(phen-NH₂) (bpy)₂]²⁺ (bpy =2,2′-bipyridine, phen =1,10-phenonthroline-5-amine). The [(bpy)₂Ru(phen-NH-)]-polydiacetylene absorbed a wide range of visible light because of the presence of two chromophores, the Ru complex and polydiacetylene. The polyacetylene backbone was converted from blue to red by conformational changes under the catalytic reaction conditions in a buffer solution. The electron transfer from the photoexcited [Ru(phen)(bpy)₂]²⁺ to the polydiacetylene backbone was observed. In a visible light-driven photocatalytic NAD⁺ reduction by (cyclopentadienyl)Rh(bpy)(H₂O)²⁺ with [(bpy)₂Ru(phen-NH-)]-polydiacetylene, NADH was regenerated, and the reactivity using Ru(bpy)₂(phen-NH)-polydiacetylene was enhanced relative to control experiments using only [Ru(phen)(bpy)₂]²⁺ or polydiacetylene. The consecutive carbon dioxide reduction coupled with formate dehydrogenase was carried out to utilize the in situ photoregenerated NADH catalytically. The catalytic condition using [(bpy)₂Ru(phen-NH-)]-polydiacetylene also showed much higher reactivity than the controls.