A Tiny Excited-State Barrier Can Induce a Multiexponential Decay of the Retinal Chromophore: A Quantum Dynamics Investigation

摘要

The N-alkyl protonated Schiff base of retinal (PSBR) is the chromophore of rhodopsin proteins,[1]-[3] a large class of transmembrane photoreceptors comprising the human retina visual pigment rhodopsin (Rh) and the bacterial proton pump bacteriorhodopsin (bR). In these receptors, PSBR undergoes an efficient cis-trans photoisomerization (e.g., the 11-cis to all-trans isomerization marked with a curved arrow in Scheme 1) which, ultimately, triggers a conformational change of the protein. It has been established that in solution the excited-state decay of PSBR is multiexponential and shows a fast (subpicosecond to picosecond) and a slow (picosecond) component, whose values depend on the type of signal recorded, the probing wavelength, and the nature of the solvent.[4]-[7] More recently, evidence for multiexponential excited-state decay has also been reported for Rh[8], [9] and bR.