S. Yamaguchi et H. Hamaguchi, FEMTOSECOND ULTRAVIOLET-VISIBLE ABSORPTION STUDY OF ALL-TRANS-]13-CIS-CENTER-DOT-9-CIS PHOTOISOMERIZATION OF RETINAL, The Journal of chemical physics, 109(4), 1998, pp. 1397-1408
The all-trans --> 13-cis.9-cis photoisomerization reaction of retinal
in aerated nonpolar solvents has been studied by femtosecond time-reso
lved ultraviolet-visible (UV-VIS) absorption spectroscopy. The excited
-state absorption spectra in the wavelength region 400-800 nm indicate
that there is no all-trans --> 13-cis.9-cis isomerization reaction pa
thway that is complete in the electronic excited singlet manifold of S
-1, S-2, and S-3. The ground-state bleaching recovery of all-trans ret
inal monitored in the near UV (ultraviolet) wavelength region 310-390
nm shows that a perpendicular excited singlet state (p) takes part in
the all-trans --> 13-cis.9-cis isomerization reaction. The lifetime o
f p is about 7 ps, and the precursor of p* is most probably the S-2 s
tate. The isomerization quantum yield derived from the femtosecond UV
absorption data agrees well with those determined by the HPLC analysis
of the photoproduct. The temperature dependence of the isomerization
quantum yield indicates the existence of a potential-energy barrier as
high as (1.2 +/- 0.6) x 10(3) cm(-1) on the reaction pathway from the
S-2 state to the p state. (C) 1998 American Institute of Physics.