High-resolution electron-energy-loss spectra of thiophene and bithiophene have been measured in the range of the low-lying singlet–triplet excitations. In combination with ab-initio calculations the observed vibrational structure within the S0 → T1 and S0 → T2 bands of thiophene is assigned and adiabatic transition energies are determined. The study of bithiophene aimed at the search for the S0 → T2 band. This transition has not been unambiguously located. The adiabatic S0 → T1 energy of thiophene, together with previous results from literature, yields a consistent set of solid phase data that can be used to model the chain length dependence of S0 → T1 excitation energies in oligothiophenes. Based on this data set and others, currently used extrapolation procedures aiming at a prediction of polymer excitation energies are evaluated. In addition, it is shown that recent semiempirical calculations do not correctly describe the convergence of the S0 → T1 energies towards infinite chain length. It is therefore advisable to apply suitable modern ab-initio methods to this problem.
No takes yet. Share an insight, caveat, or question.
Haberkern et al. (2003) studied this question.