The femtosecond absorption spectroscopy of bacteriorhodopsin was studied in the wide spectral region (450 - 900 nm) and the primary photoprocesses of the neutral purple form and the acidic blue form were compared. At neutral pH the stimulated emission at 860 urn and the excited state absorption at 480 tim decayed synchronously with a time constant of 500 fs. Thus we obtained a conclusive support for previous assignments of the transient species ''460'' being the S1 state in hR568. At acidic pH the decay kinetics of the stimulated emission at 6O nm and the excited state absorption at 480 nm were described with two time constants 1. 5 0. 2 ps and 8. 6 0. 9 ps. These two components are presumably due to the two bR isomers that exist in the blue form. Even at acidic pH no clear time-dependent oscillatory behavior was found in the stimulated emission or excited state absorption. This result shows that the isomerization around C1C14 of the retinal molecule in the S1 state is described by the over-damped oscillation. That is the isomerization angle varies only monotonously in the S1 state. 1.

Date Published: 1 May 1991
PDF: 10 pages
Proc. SPIE 1403, Laser Applications in Life Sciences, (1 May 1991); doi: 10.1117/12.57310

Published in SPIE Proceedings Vol. 1403:
Laser Applications in Life Sciences
Sergei A. Akhmanov; Marina Yu. Poroshina, Editor(s)