Relaxation dynamics of excitons in J-aggregates revealing a two-component Davydov splitting

Abstract The J-aggregates of the thiacarbocyanine dye THIATS revealing a clear-cut two-component Davydov splitting have been investigated by different optical methods. The presence of two molecules per unit cell was proved both by polarised fluorescence and linear dichroism in the absorption of aligned aggregates in a rotating cell. The fluorescence excitation spectrum of the aggregates and their quantum yield (QY) were measured across the entire exciton band. The QY was found to be 0.1 and 0.4 for excitation via the upper and lower Davydov components respectively. The radiative lifetime of emission of the J-band was estimated to be about 15 ns combining fluorescence decay data with the fluorescence quantum yield. The excitation intensity dependence of the fluorescence decays suggests the occurrence of exciton–exciton annihilation (EEA). EEA occurs even at an excitation photon fluxes below 10 10 photons/(pulse cm 2 ) corresponding to less than one absorbed photon per 10 6 monomer units.