Synthesis and spectral characterization of new 1,3,5-triaryl-2-pyrazolines highlighting effect of alkyloxy chain length on fluorescence.

A series of new 1,3,5-triaryl-2-pyrazolines (1b-12b) having one to twelve carbon alkyloxy side chains were synthesized and characterized on the basis of their spectral (IR, (1)H &(13)C NMR and GC-MS) and microanalytical data. The UV-Vis and emission spectroscopy was used to study the effect of alkyloxy chain length on absorption and fluorescence properties of 1b-12b. All the compounds showed fluorescence in the blue region of the visible spectrum. Interestingly, the alkyloxy chain length strongly affects the emission intensity of 1,3,5-triaryl-2-pyrazoline framework without causing any major blue- or red-shift in the emission wavelength (λmax(em)). The absorption and emission maxima (λmax(abs) &λmax(em)) for compounds (1b-12b) were observed in the range of 337-364nm and 454-464nm, respectively. Furthermore, the effect of fluorine substituent on aryl ring present at 3-position of pyrazoline moiety on fluorescence properties is also discussed.