Wavelength Regulation in Visual Pigment Chromophore: Large Induced Bathochromic Shifts in Retinol and Related Polyenes.*

Low temperature techniques are used to record spectra of long wavelength absorbing electrochromic species formed from retinol and related compounds. Formation of these electrochromic species is induced either by iodine or trichloroacetic acid which merely act as acids. The electrochromic species are the corresponding carbonium ions of the respective polyenes. The resulting carbonium ions of a given polyene are identical regardless of whether they are formed by iodine or trichloroacetic acid. The molecular structures of the carbonium ions can be written with certainty. Consequently, the exact nature of the π‐electron system in the polyene and its carbonium ion may be elucidated.