The preparation and spectral properties of some monosubstituted 1,3,5,-Triphenyl-2-pyrazolines

Abstract

A large number of mono-para-substituted 1,3,5-triphenyl-2-pyrazolines and some related compounds has been synthesized, and their absorption and fluorescence properties in cyclohexane and in methanol measured. The effect of substituent on these properties and on the fluorescent whitening ability of the 1,3,5-triphenyl-2-pyrazolines in general is discussed. The presence of electron-withdrawing substituents, viz., cyano, methylsulfonyl or methoxycarbonyl groups in the para-position of the phenyl rings, has a dramatic effect on the absorption and the fluorescence properties. Such substituents located (a) in the l-phenyl ring give pyrazolines exhibiting brilliant blue fluorescence both in methanolic and cyclohexane solution, (b) in the 3-phenyl ring give highly fluorescent yellow compounds which can be considered as dyes and (c) in the 5-phenyl ring cause drastic quenching of the fluorescence.