COMPREHENSIVE EXPERIMENTAL INVESTIGATION OF EMISSION SPECTRAL PROPERTIES OF POLYENALS AND POLYENGNES RELATED TO VISUAL CHROMOPHORES

Author Institution: Department of ChemistryThe emission spectral behavior of homologs and analogs of retinals, with the number (n) of double bonds ranging from 2 to 10, has been investigated in detail as a function of chain length. In some specific cases, the effects of solvents, temperature, concentration and various hydrogen-bonding agents on photophysical properties have been studied. The polyenals/polyenones with short chain length (n= 2-4) are non-emitting with a $^{1}(n, \Pi^{*}$) state lowest; those with intermediate chain length (n= 5,6) exhibit fluorescence at $77^{*} K$ which is strongly dependent upon the exciting wavelengths and is sensitive to environmental factors and finally, those with long chain length (n= 7,8) show fluorescence (both at $298^{\circ}\, K$ and $77^{\circ}\,K$) with intensity essentially independent of exciting wavelengths. The factors contributing to the excitation wavelength dependence of flourescence intensity and the nature of the lower-lying states and the lowest-lying singlet excited state in the various polyene systems will be discussed