A femtosecond fluorescence study of vibrational relaxation and cooling dynamics of UV dyes.
We present a femtosecond broad-band fluorescence up-conversion study of the vibrational relaxation dynamics of two UV chromophores, 2,5-diphenyloxazole (PPO) and para-terphenyl (pTP), pumped with a large excess of vibrational energy (>2000 cm(-1)). The band narrowing of the transient fluorescence spectrum reflects a biphasic cooling process in a few hundreds of fs and a few ps. In the sub-ps regime, our data suggest a structural rearrangement in the excited state, followed by thermalization of the excess energy. These dynamics affect the fluorescence spectra of PPO and pTP in different ways. In PPO, the damping of a low frequency vibrational wavepacket and a significant sub-ps narrowing of the band characterize the vibrational relaxation. In pTP, the latter is faster and appears as a red shift with distortion of the band in <200 fs.
Laboratory of ultrafast Spectroscopy, ISIC, Ecole Polytechnique Fédérale de Lausanne, Switzerland CH-1015.
Olivier
O
Braem
Thomas J
TJ
Penfold
Andrea
A
Cannizzo
Majed
M
Chergui
D003080:Cold Temperature; D004396:Coloring Agents / Q000737:chemistry*; D010080:Oxazoles / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013730:Terphenyl Compounds / Q000737:chemistry*; D013997:Time Factors; D014732:Vibration
D004396:Coloring Agents; D010080:Oxazoles; D013730:Terphenyl Compounds; C009012:2,5-diphenyloxazole