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MO: Molekülphysik
MO 42: Excitation and Coherence Decay
MO 42.8: Talk
Wednesday, March 15, 2006, 15:45–16:00, H12
Vibrational relaxation and wavepacket motion in electronically excited perylene dyes in solution — •Patrizia Krok, Ida Z. Kozma, Stefan Lochbrunner, and Eberhard Riedle — LS für BioMolekulare Optik, Ludwig-Maximilians-Universität München
We study the S1 state vibrational dynamics of perylenbisimid dyes in solution. The absorption spectrum and the emission spectrum show a well structured progression that is mainly due to a single vibration. By selective excitation of the first three vibronic levels and probing at suitable wavelengths, we find a time constant of about 2 ps for the vibrational reorganization in the nonyldecyl bisubstituted dye S-19. We attribute this time constant to internal vibrational redistribution as well as relaxation to the solvent, i.e. the population decay of the optically excited vibrational level.
A complementary experiment investigates the ultrafast wavepacket motion in S-19 and related dyes to identify the Franck-Condon active modes and their dephasing and decay mechanism. We create a superposition of vibronic states with spectrally broad 11-fs pulses at 510 nm and detect oscillations at about 500, 1300 and 1500 cm−1 with 10-fs probe pulses centered in the emission region. The vibrational frequencies are compared to calculations and measurements in helium nano droplets [1]. The decay of the wavepacket motion allows us for the first time to decide whether pure vibrational dephasing is a significant contribution in addition to the population decay.
[1] M. Wewer and F. Stienkemeier, Phys.Chem.Chem.Pys. 7, 1171 (2005)