Sustainable Carbon Dioxide Reduction of the P3HT Polymer-Sensitized TiO 2 /Re(I) Photocatalyst.

In this study, a p -type π-conjugated polymer chain, poly(3-hexylthiophene-2,5-diyl) ( P3HT ), was physically adsorbed onto n -type TiO 2 nanoparticles functionalized with a molecular CO 2 reduction catalyst, (4,4-Y 2 -bpy)Re I (CO) 3 Cl (ReP, Y = CH 2 PO(OH) 2 ), to generate a new type of P3HT -heterogenized hybrid system ( P3HT /TiO 2 /ReP), and its photosensitizing properties were assessed in a heteroternary system for photochemical CO 2 reduction. We found that P3HT immobilization on TiO 2 facilitated photoinduced electron transfer (PET) from photoactivated P3HT * to the n -type TiO 2 semiconductor via rapid interfacial electron injection (∼65 ps) at the P3HT and TiO 2 surface interface ( P3HT * → TiO 2 ). With such effective charge separation, the heterogenization of P3HT onto TiO 2 resulted in a steady electron supply toward the co-adsorbed Re(I) catalyst, attaining durable catalytic activity with a turnover number (TON) of ∼5300 over an extended time period of 655 h over five consecutive photoreactions, without deformation of the adsorbed P3HT polymer. The long-period structural stability of TiO 2 -adsorbed P3HT was verified based on a comparative analysis of its photophysical properties before and after 655 h of photolysis. To our knowledge, this conversion activity is the highest reported so far for polymer-sensitized photochemical CO 2 reduction systems. This investigation provides insights and design guidelines for photocatalytic systems that utilize organic photoactive polymers as photosensitizing units.