Dephasing-induced damping of superradiant emission in J-aggregates

Abstract

Results of temperature-dependent accumulated photon echo, fluorescence lifetime and fluorescence quantum yield measurements are reported on aggregates of the dye pseudoisocyanine bromide in an ethylene glycol/water glass. The results show that the lowest excited state of the J-aggregate can be described as a superradiative exciton, whose radiative and optical coherence lifetime are determined by dephasing processes. The results further indicate that the phonon-induced fluctuations of the site energies must be highly correlated. The observed discrepancy between the low-temperature photon echo decay time of 16 ps and fluorescence lifetime of 70 ps is ascribed to observation of dephasing of an excitonic wave packet in the echo and incoherent relaxation of the same k-states in the fluorescence.