Relaxation dynamics in the excited electronic state (S-1) of LDS-821 have b
een studied in aprotic and alcoholic solvents with pico- and subpicosecond
time resolution using pump-supercontinuum probe transient absorption techni
que. Steady-state absorption and fluorescence as well as the time resolved
transient absorption/stimulated emission spectra and the temporal dynamics
monitored at different wavelengths mainly reveal the features of a two-mode
kinetic process in the S-1 state-conversion of the locally excited (LE):st
ate to the twisted intramolecular charge-transfer (TICT) state. A short (<1
ps) rise time of stimulated emission monitored at the shorter wavelength b
and, is the signature of the barrierless skeletal stretching motion along t
he "valley-like" region of the potential energy surface (PES) of the SI sta
te in the Franck-Condon CFC) region to attain a metastable untwisted config
uration, called the LE state. The decay time of the LE state is equal to th
e rise time measured at the longer wavelength band, assigned to the TICT st
ate. The linear dependence of the rate of the LE --> TICT conversion proces
s on the inverse of viscosity of the solvent indicates that this low-energy
barrier crossing process is accompanied by a torsional motion about the fr
ee double bond of the molecule. The solvation time of the TICT state in dif
ferent solvents has been seen to be nearly equal to the growth lifetime of
the TICT state but much shorter than the longitudinal relaxation time of th
e solvent. These facts indicate that the rate of the LE --> TICT process is
mainly controlled by the contribution from the intramolecular modes rather
than the solvation.