The Optical Dynamics of Excitons in Cylindrical J-Aggregates

Abstract

The optical dynamics of excitons in cylindrical 5,5‘,6,6‘-tetrachloro-1,1‘-diethyl-3,3‘−di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC)/C8O3 aggregates have been investigated by ultrafast pump−probe spectroscopy and accumulated photon echo experiments. In the nonlinear optical interactions, both the one-exciton band and the two-exciton band are excited. The interpretation of the results involves the separation of the two-exciton states into two types: those that have predominantly “ring”-character, with energy separations determined by the circumference of the cylinder, and those that have predominantly “longitudinal”-character, with energy separations determined by the coherence length of the excitons along the length of the cylinder. At 1.5 K, the excitons were found to be delocalized over an area of, on average, 95 molecules. These excitons can move incoherently to other localized regions on the cylinder, leading to rapid relaxation within the one-exciton band.