Mechanism for giant electrooptic response of excitons in porphyrin J-aggregates: Molecular rearrangement model

We propose possible mechanisms for the highly enhanced electrooptic response by formation of J-aggregates observed for porphyrin molecules. For J-aggregates, the signal intensity deviates from the quadratic dependence on the electric field to show saturation behavior for a high field, while that for monomers obeys the quadratic dependence, as expected for the Kerr response. This phenomenon can be explained by the molecular rearrangement model, where the dipole–dipole interaction energy is modified by field-induced change in the angle between the molecular transition dipole moment and the aggregation axis. A possible contribution of charge-transfer states to the electrooptic response is also evaluated.