Transition dipole moments of charge transfer excitations in one-component molecular crystals

Owing to the peculiar structure of oligothiophene crystals, their low-energy b -polarized spectra are dom- inated by the contributions from charge transfer states almost free from Frenkel state admixtures, offer- ing a unique opportunity for in-depth studies of the former. Here, a simple model, rooted in the Mulliken theory of charge transfer transitions, is proposed to estimate the relevant transition dipole moments. For sexithiophene, the resultant estimate agrees with the value used in the recent detailed theoretical repro- duction of the absorption and electroabsorption spectra, and is found to be consistent with other input parameters. The approach presented here is readily applicable for other one-component molecular crys- tals, providing a simple method to estimate the intrinsic transition dipoles of charge transfer configurations