Synthesis and spectral characterization of new homologous 1,3,5-triaryl-2-pyrazolines: Influence of alkyloxy chain length on fluorescence

• Organic fluorescent compounds are important and attracted considerable attention.
• New 1-(3,4-dimethylphenyl)-3-(4-chlorophenyl)-5-(4-alkoxyphenyl)-2-pyrazolines.
• Synthesis and fluorescence property evaluation.
• Effect of chloro and alkyloxy substituents on fluorescence.

Twelve new homologous 1,3,5-triaryl-2-pyrazolines (1c–12c) have been synthesized and characterized on the basis of their spectral (IR, 1H and 13C NMR and MS) data and microanalysis. The influence of alkyloxy chain length on absorption and fluorescence properties of 1c–12c was studied by UV–Vis and emission spectroscopy. For all the compounds, fluorescence was observed in the blue region of the visible spectrum. Furthermore, a strong influence of alkyloxy chain length was found on the emission intensity of 1,3,5-triaryl-2-pyrazolines, without causing any major blue- or red-shift in the emission wavelength (λmaxem). The absorption and emission maxima (λmaxabs and λmaxem) for all the compounds were observed in the range of 408–416 nm and 471–476 nm, respectively. The effect of chloro-substituent present on the conjugated backbone of 1,3,5-triaryl-2-pyrazoline moiety is also discussed.

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