The Influence of Substituents on 4-Amino-1,2,4-Triazole Luminescence: A Combined Crystallographic and Spectroscopic Study.

To explore new luminescent materials, two novel luminescent salts, [HAD]⁺BSA⁻∙methanol (1) and [HAD]⁺TSA⁻∙methanol (2), incorporating the 4-amino-1,2,4-triazole functional moiety (AD = 4,4'-(4-amino-4H-1,2,4-triazole-3,5-diyl)dianiline), were successfully synthesized through reactions with benzenesulfonic acid and p-toluenesulfonic acid, respectively. Comprehensive characterization via single-crystal X-ray diffraction, FT-IR, UV-Vis, and PXRD revealed distinct photophysical properties governed by their supramolecular architectures. Solid-state emission studies demonstrated blue-shifted maxima at 443 nm for salt 1 and 449 nm for salt 2 compared to the free AD ligand (457 nm), corresponding to shifts of 14 nm and 8 nm, respectively. This emission modulation directly correlates with π∙∙∙π stacking interactions, where shorter stacking distances in salt 1 (3.878 Å) versus salt 2 (4.406 Å) enhance intermolecular electronic coupling. Hirshfeld surface analysis confirmed stronger C∙∙∙H contacts in salt 1, consistent with its more pronounced stacking interactions and shorter emission wavelength. The lifetimes can be observed to 1.41, 0.96 and 0.90 ns, while the quantum yields of compounds can be found to be 0.20, 0.26 and 0.38 for AD, 1 and 2, respectively. The study establishes definitive structure-property relationships, demonstrating that strategic manipulation of weak intermolecular forces provides an effective pathway for engineering luminescent properties in triazole-based materials through crystal engineering.