Spectroscopy of polyenes. 5. Absorption and emission spectral properties of polyene acids/esters related to retinoic acid/ester as homologues

A number of all-trans polyene acids and esters with chain lengths varying over a range including two longer and two shorter homologues of retinoic acid/ester have been studied for their spectral and photophysical properties. The polyene acids form intermolecularly hydrogen-bonded dimers in nonpolar solvents (3-methylpentane and carbon tetrachloride). Upon increasing the polyene chain length as well as upon dimer formation (in the cases of the polyene acids), pronounced changes occur in the absorption-emission spectral maxima, infrared absorption frequencies (carbonyl and hydroxyl stretching), and fluorescence lifetimes and quantum yields. The photophysical dynamics is discussed in terms of a fluorescing state that is primarily of 1A/sub g/*- character (dipole forbidden) in the longer polyene systems. 29 references, 5 figures, 2 tables