LOW RESOLUTION OPTICAL SPECTROSCOPY OF RETINYL POLYENES: LOW LYING ELECTRONIC LEVELS AND SPECTRAL BROADNESS*

Abstract— Optical absorption and emission spectra of retinal, axerophtene, anhydrovitamin A, and 2,10-dimethylundecapentaene in rigid glass matrixes at 77°K are presented. An interpretation of the observed spectra which provides a rationalization on the basis of electronic structure for the diffuse nature of the retinal spectrum is discussed. For the undecapentaene a weakly absorbing ¹ A _g state was found 3250 cm^-1 lower in energy than the level responsible for the strong visible absorption.