M. Enescu et al., PHOTOPHYSICS IN THE PICOSECOND TIME RANGE OF THE METHYLENE-BLUE GUANOSINE-5'-MONOPHOSPHATE COMPLEX, Journal of photochemistry and photobiology.B, Biology, 22(2), 1994, pp. 165-169
The complex of methylene blue with guanosine-5'-monophosphate was stud
ied by transient absorption laser spectroscopy with 1 ps resolution. T
he prompt transient spectrum was found to be similar to that of the fr
ee dye, while the excited-state lifetime is strongly reduced. Identica
l decays for S-1-->S-n absorption, ground-state bleaching and stimulat
ed emission were obtained. The biexponential decay (lifetimes 8 and 16
0 ps, respectively) was found to be associated with time-independent s
hapes of these transient spectra. We conclude that the observed lifeti
me shortening is due to the enhancement of non-radiative transitions b
etween S-1 and S-0 by involvement of a low-lying charge transfer state
, rather than to an electron transfer process with complete charge sep
aration.