The triggering process of rhodopsin activation leading to visual transduction has remained a key problem in the chemistry of vision. In order to provide probes to explore this process, retinal analogs ret8 3 and ret9 4, with the 11-ene cis-locked by 8- and 9-membered rings, have been synthesized. These could lead to pigment analogs which mightaccomodate a transoid chromophore upon irradiation, thus providing unique models for rhodopsin activation studies. Enzyme asays and flash photolysis of rhodopsin analogs incorporating ret8 and other retinal analogs showed that the triggering process requires complete 11-cis to trans isomerization involving the entire polyene moiety. The syntheses of ret8 3 and ret9 4 double bond isomers are described