AGGREGATION BEHAVIOR OF MIXED FLUOROCARBON AND HYDROCARBON MOLECULES IN AQUEOUS-ORGANIC SOLVENTS - NONIDEALITY AND IDEALITY OF MIXING

The emission spectra of naphthalene labeled hydrocarbons (NpHCn) and f luorocarbons (NpFCn) and anthracene labeled hydrocarbons (AnHCn) and f luorocarbons (AnFCn) in aqueous organic mixed solvents were investigat ed. The fluorescence spectrum of NpHC16 in dimethyl sulfoxide-water (D MSO-H2O) is dominated by excimer emission due to formation of aggregat es. Addition of a fluorocarbon compound with chain length of seven per fluoromethylenes results in a reduction in the excimer emission and an enhancement of monomer emission, suggesting formation;of coaggregates . In contrast, addition of a perfluorocarbon compound with chain lengt h of 12 perfluoromethylenes results in no change in the fluorescence s pectrum of NpHC16. Similarly, NpFC7 and NpFC12 in DMSO-H2O also exhibi t excimer emission exclusively. Fluorescence studies show that hydroca rbon compounds coaggregate with NpFC7 but do not coaggregate with NpFC 12. Selective excitation of the naphthalene moiety in the mixture solu tion of NpHC16 with AnFC7 or in the mixture solution of NpFC7 with AnH C12 exclusively leads to the emission of the anthracene moiety, sugges ting that efficient energy transfer between the naphthalene and the an thracene chromophores occurs. On the other hand, for the mixture of Np HC16 with AnFC12 or NpFC12 with AnHC12, no energy transfer was detecte d. All these observations indicate that fluorocarbon compounds with sh ort chains can mix with hydrocarbon compounds ideally, while those wit h long chains behave nonideally. The mixed critical aggregation concen trations of NpHC16 with NpFC7 and with NpFC12 are measured as a functi on of overall composition of the mixtures, which give insight into the magnitude of the nonideality of the mixings.