Solvent effects on the excited-state processes of XXXX : a femtosecond time-resolved absorption study.

@entity13479 @entity1042 @entity1626 @entity7170 @entity1110 @entity653 @entity36314
The excited-state dynamics of @entity36314 , a @entity7170 -like compound and, as substrate of the @entity1110 / @entity36314 oxidoreductase, a precursor of chlorophyll biosynthesis, is studied by femtosecond absorption spectroscopy in a variety of solvents, which were chosen to mimic different environmental conditions in the oxidoreductase complex. In the polar solvents @entity1042 and @entity1626 , the excited-state dynamics differs significantly from that in the nonpolar solvent @entity13479 . In @entity1042 and @entity1626 , the relaxation dynamics is multiexponential with three distinguishable time scales of 4.0-4.5 ps for vibrational relaxation and vibrational energy redistribution of the initially excited S1 state, 22-27 ps for the formation of an intermediate state, most likely with a charge transfer character, and 200 ps for the decay of this intermediate state back to the ground state. In the nonpolar solvent @entity13479 , only the 4.5 ps relaxational process can be observed, whereas the intermediate intramolecular charge transfer state is not populated any longer. In addition to polarity, solvent viscosity also affects the excited-state processes. Upon increasing the viscosity by adding up to 60% @entity653 to a methanolic solution, a deceleration of the 4 and 22 ps decay rates from the values in pure @entity1042 is found. Apparently not only vibrational cooling of the S1 excited state is slowed in the more viscous surrounding, but the formation rate of the intramolecular charge transfer state is also reduced, suggesting that nuclear motions along a reaction coordinate are involved in the charge transfer. The results of the present study further specify the model of the excited-state dynamics in @entity36314 a as recently suggested (Chem. Phys. Lett. 2004, 397, 110).
