Spectroscopic and photochemical studies of model visual pigment chromophores

The primary step in the bleaching sequence of visual pigments has been shown to occur in picoseconds, while the isomerization of model visual pigment chromophores, protonated 11‐cis retinylidene Schiff bases, takes place on a time scale several orders of magnitude slower. Thus, the well‐accepted notion that the primary step in visual transduction involves a simple isomerization deserves closer examination. Studies of visual pigments and compounds which mimic visual pigment chromophores are discussed in terms of several alternatives for the nature of the primary step. In addition to discussion of photochemical studies, spectroscopic experiments are discussed. To fundamentally understand the nature of the primary processes in visual transduction it is important to understand the photochemistry, and therefore the electronic structure, of pigment chromophores. Spectroscopic studies aimed at elucidating the electronic structure of polyenic systems are thus discussed.