Inter- and Intramolecular Processes in Organic Solutions under Excitation in the Vacuum Ultraviolet

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Abstract
The efficiency of energy transfer from solvent to solute is investigated as a function of solute concentration and excitation wavelength for solutions of diphenyloxazole in benzene, toluene, cyclohexane, and hexane. The results for benzene and toluene are similar but different from those for cyclohexane and hexane. For the first pair of solvents energy transfer takes place almost exclusively from the first excited level for all wavelengths of excitation; only for higher acceptor concentrations does the direct transfer from higher levels become noticeable. The transfer efficiency from the first excited level depends, however, strongly on the electronic level which has been initially excited. The effect of dilution of the transferring solvent is studied. For cyclohexane and hexane two or more transfer mechanisms or transferring species seem to be significantly involved even for low acceptor concentrations. The quenching effect of carbon tetrachloride and of chloroform is investigated for benzene and toluene and that of oxygen for all four solvents. While quenching of benzene and toluene by oxygen is primarily “dynamic” the quenching effect in cyclohexane and hexane is “static.” The results are compared with available results for excitation with high-energy radiation.