Dynamics of higher photoexcited states in m-LPPP probed with sub-20 fs time resolution

We study the enhanced charge generation from higher excited states in a conjugated polymer via a modification of transient differential transmission spectroscopy. The first excited state S-1 is reexcited via a second laser pulse towards a higher state S-n The relaxation dynamics of S, as well as the kinetics of the states created from S-n is revealed by a broad-band probe pulse. The push and probe durations below 20 fs allow the time-resolution of the S-n relaxation and enables us to identify the two main contributions to enhanced charge generation from S-n, energy migration and vibrational relaxation.