Trends in Conjugated Chalcogenophenes: A Theoretical Study.

Heavy atom substitution in chalcogenophenes is a versatile strategy for tailoring and ultimately improving conjugated polymer properties. While thiophene monomers are commonly implemented in polymer designs, relatively little is known regarding the molecular properties of the heavier chalcogenophenes. Herein, we use density functional theory (DFT) calculations to examine how group 16 heteroatoms, including the radioactive polonium, affect polychalcogenophene properties including bond length, chain twisting, aromaticity, and optical properties. Heavier chalcogenophenes are more quinoidal in character and consequently have reduced band gaps and larger degrees of planarity. We consider both the neutral and radical cationic species. Upon p-type doping, bond length rearrangement is indicative of a more delocalized electronic structure, which combined with optical calculations is consistent with the polaron-model of charge storage on conjugated polymer chains. A better understanding of the properties of these materials at their molecular levels will inevitably be useful in material design as the polymer community continues to explore more main group containing polymers to tackle issues in electronic devices.