In this study, a p-type π-conjugated polymer chain, poly(3-hexylthiophene-2,5-diyl) (P3HT), was physically adsorbed onto n-type TiO2 nanoparticles functionalized with a molecular CO2 reduction catalyst, (4,4-Y2-bpy)ReI(CO)3Cl (ReP, Y = CH2PO(OH)2), to generate a new type of P3HT-heterogenized hybrid system (P3HT/TiO2/ReP), and its photosensitizing properties were assessed in a heteroternary system for photochemical CO2 reduction. We found that P3HT immobilization on TiO2 facilitated photoinduced electron transfer (PET) from photoactivated P3HT* to the n-type TiO2 semiconductor via rapid interfacial electron injection (∼65 ps) at the P3HT and TiO2 surface interface (P3HT* → TiO2). With such effective charge separation, the heterogenization of P3HT onto TiO2 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 TiO2-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 CO2 reduction systems. This investigation provides insights and design guidelines for photocatalytic systems that utilize organic photoactive polymers as photosensitizing units.
Keywords: P3HT polymer sensitization; TiO2 semiconductor; heterogeneous catalysis; photocatalytic CO2 reduction; polymer/TiO2 composite.