Optical Dynamics of Condensed Molecular Aggregates:An Accumulated Photon-Echo and Hole-Burning Study of the J-Aggregate

Accumulated photon-echo and hole-burning experiments on the well-known J-bands of pseudoisocyanine bromide in an aqueous ethylene glycol glass are reported. From the low-temperature photon-echo decay of ≈ 14 ps and the assumption that this lifetime is purely radiative, the mean number of molecules in the aggregates is calculated to be about 500. It is shown that the temperature-activated optical dynamics of the excitonic J-bands can best be explained by invoking the presence of a pseudo-localized degree of freedom of ≈9 cm-1. It is concluded that photoionization is the primary process that causes hole burning of the J-bands and that the charge-separated state forms the bottleneck in the optical pumping cycle