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.