Exciton–exciton annihilation in linear molecular aggregates at low temperature

Exciton–exciton annihilation is observable in linear molecular aggregates at low temperature as the pump intensity rises in spite of the fact that, due to weak exciton–phonon coupling, the exciton mobility at low temperatures is expected to be slow. Under the circumstances outlined, the applicability of the bimolecular theory, which implies the approach of two excitons before they annihilate, seems to be questionable. We propose an alternative channel of excitonic annihilation expected to be an appropriate candidate in treating this effect and in estimating the corresponding rate. It appears to be inversely proportional to the cube of the localization length and reasonably fits the experimental data.