Calculations of the optical lineshapes for disordered molecular aggregates: effects of aggregate structure

The optical lineshapes were calculated for two-dimensional molecular aggregates in Langmuir films using our approach that increases greatly the efficiency of the numerical procedure. Calculations were performed for the aggregates with both periodic and free boundary conditions. In the case of the free boundary conditions, the calculated spectrum is found to exhibit a rather complicated structure which is due to the strong effect of the aggregate borders. Periodic boundary conditions eliminate this effect, and the absorption spectrum transforms to the single line. For this case, the dependences of the line half-width and exciton delocalization area on the disorder parameter and on the size and structure of molecular aggregate were investigated within the wide range of parameters.