SPECTROSCOPY OF POLYENES—IV. ABSORPTION AND EMISSION SPECTRAL PROPERTIES OF POLYENE ALCOHOLS RELATED TO RETINOL AS HOMOLOGUES

A number of polyene alcohols related to retinol as homologues have been examined for their spectral and photophysical properties. The absorption spectra of the polyene alcohols with short polyene chainlength show an intense band system with its maximum at 3000–4000 cm^-1 above that of the main band system. The intensity of this higher-energy band system decreases sharply as the polyene chainlength is increased. All the polyene alcohols fluoresce strongly or moderately strongly at 77 K, the intrinsic fluorescence lifetimes being significantly longer than those expected from the oscillator strengths of the main, low-energy absorption band system. Fluorescence (relatively weak) is also observed at room temperature in the cases of polyene alcohols of long chainlength. A discussion is presented regarding the possible assignments of the various observed absorption band systems, state order and nature of the lowest excited singlet state, and aggregate formation (in 3-methylpentane at 77 K) and its effect on spectral and photodynamical behavior.