New pyrazoline-imidazole derivatives as highly fluorescent small organic compounds: Synthesis, photoluminescence properties, and DFT/TD-DFT calculations

Abstract

In this paper we present the synthesis, photoluminescence properties and quantum chemical calculations of a series of novel 1,3,5-trisubstituted 2-pyrazoline derivatives incorporating an imidazole nucleus. These compounds were synthesized in good to excellent yields through the reaction of α,β-unsaturated ketones (chalcones) with phenylhydrazine derivatives. Structural elucidation of all synthesized compounds was performed using spectroscopic techniques including IR, ¹H NMR, ¹³C NMR, and HR-MS. The photoluminescence properties of the pyrazolines were evaluated using UV–visible absorption and fluorescence spectroscopy. These compounds exhibited strong fluorescence in liquid solution, with fluorescence lifetimes ranging from 3.2 ns to 4.3 ns and quantum yields between 50 % and 74 %. The absorption spectra of the compounds revealed peaks in the near-ultraviolet region (325 to 364 nm), while the emission spectra displayed wavelengths in the blue region (434 to 476 nm). Additionally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, performed at the PBE0/TZVP level of theory, provided insight into the mechanisms underlying the fluorescence properties of the synthesized molecules.