Sl. Logunov et al., The relaxation dynamics of the excited electronic states of retinal in bacteriorhodopsin by two-pump-probe femtosecond studies, P NAS US, 98(15), 2001, pp. 8475-8479
Citations number
37
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
We present the results of two-pump and probe femtosecond experiments design
ed to follow the relaxation dynamics of the lowest excited state (S-1) popu
lated by different modes. In the first mode, a direct (S-0 --> S-1) radiati
ve excitation of the ground state is used. In the second mode, an indirect
excitation is used where the S-1 state is populated by the use of two femto
second laser pulses with different colors and delay times between them. The
first pulse excites the S-0 --> S-1 transition whereas the second pulse ex
cites the S-1 --> S-n transition. The nonradiative relaxation from the S-n
state populates the lowest excited state. Our results suggest that the S1 s
tate relaxes faster when populated nonradiatively from the S-n state than w
hen pumped directly by the S-0 --> S-1 excitation. Additionally, the S-n --
> S-1 nonradiative relaxation time is found to change by varying the delay
time between the two pump pulses. The observed dependence of the lowest exc
ited state population as well as its dependence on the delay between the tw
o pump pulses are found to fit a kinetic model in which the S-n state popul
ates a different surface (called Si) than the one being directly excited (S
-1). The possible involvement of the A(g) type states, the J intermediate,
and the conical intersection leading to the S-0 or to the isomerization pro
duct (K intermediate) are discussed in the framework of the proposed model.