Abstract

The collective optical response of molecular aggregates has attracted much attention over recent years. Due to the exciton delocalization in these structures, giant transition dipoles may occur leading to ultrafast spontaneous emission and large nonlinear polarizabilities. Disorder in the transition frequencies of the molecules that make up an aggregate plays a crucial role in the exciton delocalization and, therefore, strongly affects the optical response. If the disorder a₀ is small and has no intermolecular correlations, the aggregate linear absorption spectrum is motionally narrowed and has a typical width $a_0\sqrt{\text{N}}$ with N the number of molecules in the aggregate.¹ However, motional narrowing can be strongly reduced if the inhomogeneous frequency offsets of the molecules within an aggregate are correlated. Although correlations in solvent-induced shifts of neighboring molecules are very likely, one mostly assumes totally uncorrelated disorder in model studies. The reason is that experimentally no independent information on the size and the degree of correlation of the disorder can be obtained from the width of the linear absorption spectrum.

© 1994 IEEE