"Femtosecond fluorescence and absorption dynamics of B. Schmidt, C. Sobotta, S. Malkmus, S. Laimgruber, M. Braun, W. Zinth, P. Gilch
an azobenzene with a strong push-pull substitution "
Journal of Physical Chemistry A 108 (2004) 4399-4404
The ultrafast photoisomerization of a push-pull substituted azobenzene (4-nitro-4'-(dimethylamino)azobenzene, NA) is studied by means of femtosecond fluorescence and absorption spectroscopy. The fluorescence dynamics is biphasic. The initial fluorescence with a narrow
and intense spectrum decays in ~100 fs. This decay is accompanied by the rise of broad red-shifted and much weaker emission. The same time constants recur in the transient absorption spectra which hold additional information on the ground-state dynamics. The ground state recovers in 0.8 ps, demonstrating that only the longer time constant is associated with an internal conversion process. Small spectral changes occurring thereafter (~5 ps) point to vibrational cooling in the ground state. The results are analyzed in comparison with the behavior of the parent compound azobenzene. Though the push-pull substitution of azobenzene strongly alters the character of its excited states, the photodynamics are surprisingly robust with respect to that substitution.
BMO authors (in alphabetic order):
Ultrafast Fluorescence Spectroscopy - The Kerr-Gate Setup
The flow of vibrational energy in molecules