Urea and thiourea inclusion complexes of conjugated polyenes: Polarized fluorescence excitation and resonance Raman studies

Urea and thiourea inclusion complexes have been prepared containing conjugated polyene chromophores. Dialkylpolyenes with n-alkane tails form complexes with urea; carotenoids and diphenylpolyenes form complexes with thiourea. In some cases the chromophoric groups are diluted by incorporation of saturated hydrocarbons into the inclusion complexes. The resulting crystals are highly dichroic with their maximum absorption along the crystallographic hexagonal c-axis. Polarized fluorescence excitation studies (of the urea n-alkylpolyene complexes) and polarized single crystal resonance Raman studies (of the thiourea carotenoid and diphenylpolyene complexes) have been performed and are interpreted in terms of the orientation of the transition dipole of these polyenes with respect to the molecular axis.