Poly(3,4-ethylenediselena)thiophene - the selenium equivalent of PEDOT

The first synthesis of the selenium analogue of EDOT, together with its electrochemical polymerization and redox and electronic properties of the resulting polymer, poly(3,4-ethylenediselena)thiophene (PEDST), is reported. The HOMO and LUMO values for the polymer (calculated from cyclic voltammetry experiments) are −4.8 and −3.3 eV, respectively, whereas the experimental band gap is 1.55 eV. Within the related series of polymersPEDOT, PEDTT, and PEDSTthe selenium analogue has a significantly lower LUMO value than the oxygen or sulfur derivatives (by ca. 0.55 eV). Quantum chemical calculations on trimers ((EDXT)3, where X = O, S, or Se) show that the most planar conformation within the conjugated chain is achieved by EDOT systems. However, the calculated energy of a fixed planar conformation for PEDST is 13.9 kJ mol-1 lower than the corresponding unconstrained conformer, indicating that a planar structure is preferred; this data corroborates the lower experimental band gap observed for PEDST (1.55 eV) compared to PEDTT (2.19 eV).