PHOTOPHYSICS IN THE PICOSECOND TIME RANGE OF THE METHYLENE-BLUE GUANOSINE-5'-MONOPHOSPHATE COMPLEX

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.