Double-Excitation Dynamics in m-LPPP probed with sub-20 fs Time Resolution

In a novel modification of transient differential transmission spectroscopy, the first excited state S-1 is reexcited via a second laser pulse towards a higher lying state S-n. The dynamics of the relaxation of this state S-n as well as the states created from S-n, are revealed by a broad-band probe pulse. We find that the charge carrier generation efficiency from S-n is higher compared to S-1. The push and probe durations below 20 fs enable the temporal resolution of the ultrafast relaxation of the S-n state and enables us to identify the two main contributions to enhanced charge generation from S-n, energy migration towards sites of high dissociation probability, and exciton dissociation during vibrational relaxation.