Dependence of Photochemical Reactivity of the All-trans Retinal Protonated Schiff Base on the Solvent and the Excitation Wavelength

An all-optical experimental technique aimed at measuring photoisomerization quantum yield (ϕ) of the all-trans protonated Schiff base of retinal in solution has been implemented. Upon the increase in the excitation wavelength from 400 to 540 nm a slight increase in ϕ from 0.16 ± 0.03 to 0.20 ± 0.02 is observed in the chromophore dissolved in methanol, whereas the ϕ value of the one dissolved in acetonitrile varies only from 0.22 ± 0.03 (400 nm) to 0.23 ± 0.04 (540 nm). The results suggest that dissipation of the excited-state vibrational energy excess, along with environment-induced modifications of the potential energy surfaces are necessary for an efficient retinal photoisomerization in both solvent and protein environment.