VISUAL PIGMENTS .9. FLUORESCENCE OF DIMERS OF RETINALS

Dry all-trans- and 13-cis-retinals in dry alkane solvents show no fluorescence at 77 K, ∅F<10-4, under the experimental conditions of a relatively low concentration, less than 10-5 M. However, it is found that if the concentration is high enough, 5×10-5 to 10-3 M, fluorescence occurs even for dry retinals in dry alkane solutions at 77 K. From experiments regarding the concentration dependence of the absorption and fluorescence, the fluorescence is assigned as being due to a dimer of retinal. The presence of dimers can be an additional cause of the wavelength dependence of the apparent quantum yield of fluorescence in addition to that found involving H bonding. A structure of the dimer is discussed. © 1978, American Chemical Society. All rights reserved.