Ultrafast spectroscopy of rhodopsins - Photochemistry at its best!

Recent advances in laser technology now allow us to study the ultrafast primary photochemical events in rhodopsin, bacteriorhodopsin, and halorhodopsin in real time. The results of various ultrafast studies of rhodopsins are reviewed with an emphasis on (1) the relationship between the reaction rate and reaction efficiency and its implications for the mechanism of isomerization, (2) the homogeneity of the reaction pathways, and (3) the role of the protein in the reaction dynamics. The results mandate the introduction of a new paradigm to describe these ultrafast reactions that specifically considers the importance of the timescale of vibrational dephasing and relaxation relative to the reactive motion and the contribution of vibrational coherence to the reaction mechanism.