Hybrid pyrazoline-triazole fluorescent dyes: Synthesis, photophysics, electrochemical, and antioxidative activity

Abstract

A four-step reaction method to synthesize a new series of 1-benzyl-4-((2-(1,5-diaryl-4,5-dihydro-1H-pyrazol-3-yl)phenoxy)methyl)-1H-1,2,3-triazoles (5) and their photophysical and electrochemical evaluation is reported herein. The synthetic method comprises: (i) Michael condensation between 2-hydroxy-acetophenone and aryl aldehydes to obtain chalcones, (ii) a [3 + 2] cyclocondensation reaction involving chalcones and phenylhydrazine to reach the 2-pyrazolines (1), (iii) an O-alkylation reaction of 1 with propargyl bromide (2) to give O-propargylated 2-pyrazolines 3, and (iv) standard copper-catalyzed azide-alkyne cycloaddition (CuAAC) involving benzyl azide (4) and 2-pyrazolines 3 to furnish the desired triazole series (5) as a new hybrid polycyclic system at total yields of up to 51%. Steady-state fluorescence emission exhibited a band in the blue region when excited at the least energetic transition of each compound, with varying values of fluorescence quantum yields (Φf) and Stokes Shift (SS), according to solvent polarity. In the solid state, the compounds showed similar behavior to the study of the absorption and emissive properties in solution. TD-DFT calculations revealed that all compounds had delocalized electron density along the pyrazoline unit and were not influenced by the attached substituent or change in solvent polarity. In addition, electrochemical and DPPH antioxidant analyses were performed.