Double-excitation dynamics in m-LPPP probed with sub-20 fs time resolution

摘要

We present a modification of transient differential transmission spectroscopy, where the first excited state S_1 is re-excited 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 kinetics of the states created from S_n is revealed by a broad-band probe pulse. We find an enhanced charge carrier generation from a higher lying excited state S_n. The push and probe durations below 20 fs allow the time 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 quenching sites and exciton dissociation during vibrational relaxation.