Excited-state polarizability in crystalline sexithiophene: Charge-transfer and vibronic effects

A model of vibronic coupling in a manifold of coupled Frenkel and charge transfer states is applied to evaluate the electric-field-induced shifts of lowest vibronic levels deriving from the lower Davydov component of the Frenkel exciton in sexithiophene. With respect to the isolated-molecule value, vibronic terms combined with the mixing between Frenkel and CT configurations amplify the field-induced shift by the factor of seven for the 0–0 line and by further 60% for the vibronic replica in the main progression-forming mode. Confirmation is found in the existing experimental literature.