rigid glass at 77 °K (cf Table I). Mirror symmetry was still conserved in all these solvents.There are several centers in the bicyclic ring system where interaction with a polar solvent can be envisaged, with a resultant reduction in the fine structure. This is in accord with a general trend for polar solute molecules in polar and nonpolar solvents (6).The polarity of the solvent influenced the fluorescence quantum yield to a more significant extent than the spectral solvent shifts. The variations extend from a 2-fold increase in Compound 1 to an approximately 10-fold increase in Compound 8. The quantum yields were greatest in benzene and least in DMF or ethanol. The competing excited state processes in operation in these molecules are apparently fluorescence emission (Equation 2), intersystem crossing plus deactivation (Equation 3) and internal conversion from the singlet excited state (Equation 4). iA ii-'A* (1) LA* -2 34A + hv' (2) iA* LA* -LA (3) LA* -iA (4) (6) . H. Jaffe and M. Orchin, "Theory and Applications of Ultraviolet Spectroscopy," John Wiley & Sons, New York, N. Y" 1962, p 186.Permanent photochemical reactions were not observed in these molecules even upon 2-3 weeks of continuous irradiation. The only part triplet states apparently play in these compounds is to provide a possible means of deactivation. Triplet states apparently deactivate quite rapidly as no phosphorescence was observed at 77 °K and the triplet quenchers biacetyl and piperylene were not effective in the transfer of triplet energy. In the case of biacetyl quencher, no biacetyl phosphorescence was observed in thoroughly outgassed solutions of mixtures of a representative series of Compounds 1-12 and biacetyl. In the case of piperylene no cis-trans photostationary state was obtained in Compound 1-piperylene mixture in benzene.The increased solvent polarity enhances the efficiency of internal conversion and/or intersystem crossing relative to fluorescence. The reasons for the increase in relative efficiencies of excited state processes is largely unknown and is an area under intense investigation.

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