Nonlinear optical properties of one-dimensional organic molecular aggregates in nanometer films

Nanometer films of molecular J-aggregates of pseudoisocyanine (PIC) with various degrees of both static and dynamic disorder were prepared. The amount of static disorder was varied by modifying the local environment of the J-aggregates in the films, while the dynamic disorder was varied by changing the film temperature. Through these variations, the delocalization length N-del of the excitons was controlled, as could be monitored from the width of the exciton absorption line. This has allowed us to establish the scaling of the nonlinear optical susceptibility per aggregate molecule, chi((3))/N, with the delocalization length as chi((3))/N proportional to N-del(gamma), with gamma = 2.3+/-0.2. This behavior turned out to be independent of the detailed nature of disorder, and agrees very well with the theoretically predicted size-enhancement of the cubic susceptibility in J-aggregates. (C) 2003 Elsevier B.V. All rights reserved.