KINETIC-STUDY OF THE PHOTOISOMERIZATION OF A PROTONATED SCHIFF-BASE OF 11-CIS-RETINAL OVER THE PICOSECOND-TO-SECOND TIME REGIMES

The kinetics of the photoisomerization of the protonated n-butylamine Schiff base of 11-cis-retinal dissolved in methanol was studied. Laser-flash and steady-state experiments were performed to monitor spectral changes after excitation in the ps, ns, ms, and s time regimes. Substantiation of the 11-cis to all-trans isomerization was made. From the ms experiments, no triplet transients or comparably long-lived transient species were observed. In the ns experiments, cis-to-trans isomerization was seen to occur in less than 1 ns after laser excitation. Results from the ps experiments showed that the observed lifetime of isomerization was less than 8 ps. This rapid observed isomerization rate for the protonated 11-cis Schiff base in solution is comparable to the rate seen in rhodopsin.