Molecular design of a π-conjugated single-chain electronically conductive polymer

This study demonstrates that single-chain π-conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne-type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π-conjugated systems, which partially cancel each other out. It is probable that we can design one-dimensional polymers with HOMO-LUMO gaps small enough to be conductive by combining the above-mentioned oligomers with each other as monomer units in the polymer.