Absorption spectra of dipolar Frenkel excitons in two-dimensional latticeswith configurational disorder: Long-range interaction and motional narrowing effects

We present results of numerical simulations of optical absorption line shap e of Frenkel excitons in two-dimensional disordered lattices. Disorder is g enerated by Gaussian randomness in the molecular positions. The intersite i nteraction is considered to be of dipole origin, including coupling to far neighbors. Results of simulations are compared with those obtained in the f rame of the nearest-neighbor approximation, showing remarkable differences in the absorption line shape. The motional narrowing effect is found to be essentially different from that previously reported for the case of diagona l disorder as well as for that produced by randomness in nearest-neighbor h opping integrals. (C) 2000 American Institute of Physics. [S0021-9606(00)53 105-5].