Linear absorption as a tool to measure the exciton delocalization length in molecular assemblies

Using numerical simulations, we study the possibility to determine the exci ton delocalization length in molecular aggregates from the width of the lin ear absorption spectrum. We show that, in practice, the most useful approac h is not based on the well-known exchange narrowing of the line width, but rather on the typical separation between the two lowest exciton states lyin g in one delocalization interval. We discuss the application to pseudo-isoc yanine (PTC) J aggregates and the bacterial antenna complex LH2. (C) 2000 E lsevier Science B.V. All rights reserved.