Synthesis and Structure–Property Relationship of <i>meso</i>-Substituted Porphyrin- and Benzoporphyrin–Thiophene Conjugates toward Electrochemical Reduction of Carbon Dioxide

A novel series of Zn^II-<i>trans</i>-A₂B₂ porphyrins and benzoporphyrins bearing phenyl and thiophene-based <i>meso</i>-substituents was successfully synthesized and characterized by spectroscopic and electrochemical techniques. Systematic comparison among the compounds in this series, together with the corresponding A₄ analogs previously studied by our group, led to the understanding of the effects of π-conjugated system extension of a porphyrin core through β-fused rings, replacement of the phenyl with the thiophene-based <i>meso</i>-groups, and introduction of additional thiophene rings on thienyl substituents on photophysical and electrochemical properties. Oxidative electropolymerization through bithiophenyl units of both A₄ and <i>trans</i>-A₂B₂ analogs was achieved, resulting in porphyrin- and benzoporphyrin-oligothiophene conjugated polymers, which were characterized by cyclic voltammetry and absorption spectrophotometry. Preliminary studies on catalytic performance toward electrochemical reduction of carbon dioxide (CO₂) was described herein to demonstrate the potential of the selected compounds for serving as homogeneous and heterogeneous electrocatalysts for the conversion of CO₂ to carbon monoxide (CO).