The interactions of excited 1,3-Diphenyl-2-pyrazoline with indole and phenol

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Abstract
The fluorescence emission spectrum of 1,3-diphenyl-2-pyrazoline loses its structured appearance and shifts to lower energies in the presence of indole in n-heptane. There is also a decrease in the intensity at the maximum fluorescence position. These changes are similar to those which occur when the diphenyl-pyrazoline is dissolved in solvents of increasing polarity. They are attributed mainly to a high concentration of the indole in the solvent shell of the diphenylpyrazoline and the solvent-shell reorientation processes which result from an increased dipole moment of the diphenyl-pyrazoline in the excited state and which occur in the time interval between absorption and subsequent emission. The NH group is not necessary for the interaction since l,2-dimethylindole brings about similar changes in the fluorescence spectrum of the diphenylpyrazoline. In the presence of phenol the predominant effect is a marked quenching of the fluorescence of the diphenyl-pyrazoline. This is attributed mainly to a hydrogen transfer mechanism operating between phenol and the diphenylpyrazoline.

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