Nafion-Assisted Noncovalent Assembly of Molecular Sensitizers and Catalysts for Sustained Photoreduction of CO2 to CO

The efficient coupling of light absorbers with catalysts is the most critical step in the multielectron transfer process for CO2 conversion. Here a heterogenized photoconversion system consisting of noncovalent assembly is tested and proposed. Nafion (NO polymer is employed as a simple and robust platform that couples the light absorber (Ru-(bpy)(3)(2+): RuL) and the catalyst (fac-Re(bpy)(CO)(3)Cl: Re(I)) without making any chemical linkage between them to drive the reductive conversion of CO2 to CO. The results clearly show that the ternary Re(I)-RuL-Nf system exhibits higher photoconversion of CO2 and higher photostability than those of the homogeneous Re(I)RuL system without Nf. Nf polymer backbone provides sulfonate ionic exchange sites that tightly bind cationic RuL through electrostatic attraction. The Nf-bound RuL sensitizers hinder the destructive self-sensitized reaction but enhance the chance of bimolecular electron transfer from the excited RuL to Re(I), which was confirmed by time-resolved spectroscopic analysis. The total turnover number (TON) of produced CO after 20 h reached 454 in the Re(I)-RuL-Nf system (vs TON 110 in Re(I)-RuL), which demonstrated the essential role of Nf in the photoconversion process.