Picosecond Time-Resolved Coherent Anti-Stokes Raman Spectroscopy of the Artificial Bacteriorhodopsin Pigment, BR6.11

Abstract

The picosecond molecular dynamics in an artificial bacteriorhodopsin (BR) pigment, BR6.11, are measured by picosecond time-resolved coherent anti-Stokes Raman spectroscopy (PTR/CARS) and picosecond transient absorption (PTA). The BR6.11 pigment contains a structurally modified retinal chromophore with a six-membered carbon ring bridging the C11C12−C13 bonds, which both locks the C11C12 bond in the trans configuration and prevents rotation about the C12−C13 bond. The changes in the vibrational degrees of freedom of the retinal attributable to the six-membered carbon ring are found in the picosecond resonance CARS (PR/CARS) spectrum of ground-state BR6.11. Normal mode assignments for more than forty BR6.11 vibrational features are made through comparisons with the PR/CARS data from native BR-570 (previously analyzed in terms of the selective isotopic substitution of the retinal). PTR/CARS spectra from two intermediates (J6.11 and K6.11), observed by PTA to appear during the initial 200 ps of the BR6.11 phot...