Giant Nonlinear Optical Response of Interacting One-Dimensional Frenkel Excitons in Molecular Aggregates

Experimental results for the nonlinear optical properties of thin films of molecular J-aggregates of substituted pseudoisocyanine (PIC) are reported. These molecular aggregates were found to possess a giant third-order optical nonlinearity (|χ(3)| ≈ 10–5 esu). Thin films of J-aggregates of PIC iodide with several different N-alkyl substituents were obtained to study the effect of disorder on the nonlinear optical properties. The spectral features of the nonlinear optical susceptibility are analyzed within a model that includes exciton–exciton interactions.