Structure--Property Correlations in Disubstituted 1, 2, 3-Triazoles: DFT Insights and Photophysical Analysis

The inherent structural rigidity and modifiable electronic features of disubstituted 1,2,3-triazoles are driving their recognition as adaptable frameworks in photophysical and supramolecular chemistry. The combination of structural integrity and tunable electronic characteristics makes 1,2,3-triazoles highly functional for a wide range of applications, from fluorescence-based sensors and drug design to organic electronics. Owing to the versatile applications of triazoles in multiple domains, this study integrates experimental and computational analysis of a series of 1,4- and 1,5-disubstituted 1,2,3-triazole derivatives. To elucidate the electronic architecture, photophysical characteristics, and structure–property correlations, 1,2,3-triazoles with and without a hydroxyaromatic framework have been investigated. Emphasis has been given to the molecules’ solvatochromic behavior in medium-polarity solvents. The photophysical behavior of the studied 1,2,3-triazole molecules is also modulated by pH, reflecting changes via a protonation/deprotonation pathway specific to the individual molecules. Systematic spectroscopic investigations revealed differential absorption and emission responses across acidic to basic environments, highlighting the sensitivity of triazole chromophores to proton-coupled electronic interactions. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations at the B3LYP/6-311G(d,p) level were employed to investigate the frontier molecular orbitals (FMOs), electron density distributions, and polarity of the studied molecules, with outcomes corroborated by UV–vis and fluorescence spectroscopic measurements. Additionally, Natural Bond Orbital (NBO) analysis is performed for 2-(4-phenyl-1-H-1,2,3-triazol-1-yl) phenol (PTP) and 5-anilino-4-phenyl-1H-1,2,3-triazole (APT), representing hydroxyaromatic and nonhydroxyaromatic triazoles, respectively. This analysis primarily focuses on establishing the photophysical characteristics of the molecules as being of a charge-transfer nature and their inherent electron density distribution. A comparative analysis of experimental and computational data revealed a consistent and complementary trend, reinforcing the reliability of the interpretations drawn from both approaches.