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

A novel series of Zn^II-trans-A₂B₂ porphyrins and benzoporphyrins bearing phenyl and thiophene-based meso-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 meso-groups, and introduction of additional thiophene rings on thienyl substituents on photophysical and electrochemical properties. Oxidative electropolymerization through bithiophenyl units of both A₄ and trans-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).