Optical and Computational Studies on a Triazine Derivative of Dual Fluorescence Enhancement/Superquenching Upon Nanoparticle Interactions.

Derivatives of 1,2,4-triazine have emerged as versatile scaffolds with broad pharmacological and biological potential, prompting deeper exploration of their optical behavior. In this study, we investigate the photophysical properties of a novel 1,2,4-triazine dye, 4-amino-6-(4-methoxyphenyl)-1,4,6,7 tetrahydrothieno [2,3-e] [1,2,4] triazine-3(2 H)-thione (Triazine I) with a focus on its interaction with noble metal nanoparticles. The synthesized dye was structurally characterized using FTIR, ¹H-NMR, ¹³C-NMR, and mass spectrometry to confirm its purity and molecular structure. Silver (Ag-NPs) and gold (Au-NPs) nanoparticles were synthesized via a chemical reduction method and thoroughly characterized using UV-vis spectroscopy, TEM, DLS, Zeta Potential, and XRD, confirming their successful formation, stability, and crystalline nature. Spectroscopic investigations revealed solvent-dependent absorption and emission behavior of Triazine I, along with a dual fluorescence response in the presence of nanoparticles: superquenching by Ag-NPs via non-radiative decay enhancement, and fluorescence amplification by Au-NPs through radiative enhancement (MEF). These findings open promising avenues for using such systems in advanced fluorescence-based biosensing and immunoassays. Furthermore, DFT-based computational studies provided insights into molecular geometry, electronic transitions, and electrostatic potential, reinforcing experimental observations and guiding future molecular de sign. This integrated experimental-theoretical approach highlights Triazine I as a promising candidate for tunable optical applications, particularly in bioimaging and diagnostic platforms.