Laser control of dissipative two-exciton dynamics in molecular aggregates

Abstract

There are two types of two-photon transitions in molecular aggregates: non-local excitations of two monomers and local double excitations to some higher excited intra-monomer electronic state. As a consequence of the inter-monomer Coulomb interaction, these different excitation states are coupled to each other. Higher excited intra-monomer states are rather short-lived owing to the efficient internal conversion of electronic into vibrational energy. Combining both the processes leads to annihilation of an electronic excitation state, which is a major loss channel for establishing high excitation densities in molecular aggregates. Applying theoretical pulse optimization techniques to a Frenkel exciton model, it is shown that the dynamics of two-exciton states in linear aggregates (dimer to tetramer) can be influenced by ultrafast-shaped laser pulses. In particular, we studied the extent to which the decay of the two-exciton population by inter-band transitions can be transiently suppressed. Intra-band dynamics is described by a dissipative hierarchy equation approach, which takes into account strong exciton–vibrational coupling in the non-Markovian regime.