Abstract

The light induced isomerisation of the retinal molecule (more exactly protonated Schiff base retinal, PSBR) plays an essential role in a number of important functional biomolecules like rhodopsin (responsible for vision), bacteriorhodopsin (BR, photosynthetic light induced proton pump) and halorhodopsin (HR, light induced chloride pump). These proteins were investigated in detail by femtosecond spectroscopy. In all cases, a fast S₁ reaction occurs prior to the transition to the ground state. However, the details of the photoreaction critically depend on the specific surrounding of the chromophore in the protein: The 11-cis→all-trans isomerisation in rhodopsin and the all-trans→13-cis isomerisation in BR occur extremely fast with 200 fs [1] and 500 fs [2], respectively. A slower and biexponential process is observed for the all-trans→13-cis isomerisation of HR with 1.5 ps and 8.5 ps [3]. In order to separate the influence of the protein from the intrinsic properties of the retinal molecule, isolated all-trans-PSBR (in ethanol) was investigated in the present paper. In addition to standard VIS measurements, femtosecond IR experiments will be presented in order to reveal structural aspects of the photoreaction.

© 1996 Optical Society of America