HYDROPHOBIC EFFECT ON PHOTOCHEMICAL AND PHOTOPHYSICAL PROCESSES VII. FLUORESCENCE SPECTRA AND AGGREGATION OF PYRENYL ALKYL KETONES IN POOR SOLVENTS

The monomer and excimer fluorescence spectra of pyrenyl alkyl ketones are sensitive to-environmental polarity. The monomer fluorescence in nonpolar solvents is very weak, but it becomes quite intense in polar solvents. Both monomer and excimer fluorescence maxima' show significant red shift with increasing solvent polarity. This strong dependence of fluorescence on solvent polarity is used to study aggregation of long chain molecules in dimethyl sulfoxide-water mixture. At very low concentration pyrenyl alkyl ketones with long chain show excimer fluorescence and the monomer fluorescence is blue shifted, indicating aggregate formation Saturated hydrocarbons with long chain coaggregate with these ketones. The polarity in aggregates is analogous to that in cyclohexane.