Ultrafast photophysics of the protonated Schiff base of retinal in alcohols studied by femtosecond fluorescence up-conversion

The ultrafast spectral evolution of the fluorescence of the all-trans protonated Schiff base of retinal (PSBR) in alcs. with different polarity was studied using the fluorescence up-conversion technique in a "polychromatic mode". Results reveal that vibrational cooling is the dominant contribution to the total Stokes shift of PSBR's in alcs. The total Stokes shifts are very large: 7.9 +- 100/cm for PSBR/methanol and 6.87 +- 100/cm for octanol. Another striking observation is the .apprx.30% smaller width of the fluorescence spectrum of methanol compared with other alcs. On the other hand, dielec. solvation has only minor contribution to the total Stokes shift, irresp. of the solvent. In both solvents, the time-zero spectrum is already red-shifted by more than 6.0/cm with respect to the max. of absorption. [on SciFinder (R)]