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 -A 2 B 2 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 A 4 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 A 4 and trans -A 2 B 2 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 (CO 2 ) was described herein to demonstrate the potential of the selected compounds for serving as homogeneous and heterogeneous electrocatalysts for the conversion of CO 2 to carbon monoxide (CO).