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

• 2-Pyrazolines are attractive organic fluorescent compounds.
• Synthesis of new 1-(3,4-dimethylphenyl)-3-(4-fluorophenyl)-5-(4-alkoxyphenyl)-2-pyrazolines.
• Spectral characterization and fluorescence properties.
• Effect of fluoride and alkyloxy substituents 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, 1H & 13C 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 (λmaxem). The absorption and emission maxima (λmaxabs & λmaxem) for compounds (1b–12b) were observed in the range of 337–364 nm and 454–464 nm, respectively. Furthermore, the effect of fluorine substituent on aryl ring present at 3-position of pyrazoline moiety on fluorescence properties is also discussed.

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