Determination of the electronic structure of thiophene oligomers and extrapolation to polythiophene

Ionization energies, attachment energies, and electrochemical reduction potentials of thiophene oligomers (n<1 <5 ) have beendetermined experimentally (ultraviolet photoelectron and electron transmission spectroscopies and cyclic voltammetry) and theoretically (ionization and attachment energies by MIND0/3). The geometrical parameters of the most stable conformation of 2,2'-bithienyl have been computed at the ab initio STO-3G level with complete relaxation. A short extrapolation of the energy data to the polymer provided accurate and reliable values for important properties of (gas phase) polythiophene, namely, ionization energy (6.9 eV), valence bandwidth (3.2 eV), electron affinity (0.9-1.1 eV), HOMO-LUMO energy gap (5.9 eV), and A, (2.7 eV).