A Density Functional Theory ( DFT/B۳L YP) Investigation o f Charged Thiophene Oligomers

Calculations were performed with the G aussian ۹۸ program. The basis s ets correspond to those implemented in the software. The geometries of the isolated bi-, ter-, and quaterthiophene cations were optimized with MP۲ at the ۶-۳۱۱++G** level and the relaxed struct ures used for the calc ulations of the dimers. The ʌ-stac king of oxidized thio phene oligo mers is investigated using extensive ab-initio quantum chemistry methods. Dim ers of singly-charged oligothiophen es are found to be unsta ble in the gas phase, but can be stabilized as bound dicatio ns in the singlet state by a polarizable solvent such as acetonitrile. Our calculations provide a detailed description of the mechanisms a nd the energ etics involv ed in the di merization phenomenon and highlights the role and importance of the environment in the stabilization of the stacks. Th e need for accurate treatments of e lectronic co rrelations and of solvation effects for a realistic description of these ma terials is underscored.