engleski

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

All-trans retinal is the photosensitive moiety in many retinal proteins found in halobacteria. Bacteriorhodopsin (bR) is the most prominent example, in which retinal is covalently bound to the nitrogen atom of a lysine residue forming a protonated Schiff base linkage. With this background, it is worthwhile understanding the photophysics of the retinylidene chromophore in well-characterized solvents for reference purposes. Femtosecond spectroscopy on the protonated Schiff base form of all-trans retinal in methanol has been reported. The excited state decay time has been attributed to trans-cis isomerization. However, a detailed characterization of intramolecular dynamics (IVR, internal conversion, isomerization) and a distinction from intermolecular processes depending on the solvent properties remains unaddressed until now. Signatures indicative of the fact that three different cis isomers are being formed in methanol had not been found in the kinetics. This chapter discusses the ultrafast spectral evolution of the fluorescence of the all-trans PSBR in alcohols with different polarity. It is shown, using the fluorescence up-conversion technique in a "polychromatic mode", that vibrational cooling is a dominant contribution to the total Stokes shift of PSBR''s in alcohols.

fluorescence upconversion ; ultrafast spectroscopy ; retinal ; solvent effects

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