Observation of Optical Nonlinearity Size Enhancement in One-Dimensional Molecular Aggregates

Thin films of molecular aggregates of pseudoisocyanine were obtained. Delocalization length of exciton wave function was measured with an assumption that an absorption line width is defined by disorder induced mixing of the lowest states of the one-exciton band. Predicted effect of size enhancement of the nonlinear optical properties for molecular aggregates was observed. The assumption used to determine the delocalization length is shown to coincide with the observed optical nonlinearity size enhancement phenomenon.