Photoactive benzothiadiazole-N-heterocycle derivatives: synthesis, photophysics and water sensing in organic solvents

The study reported herein describes the synthesis of benzothiadiazole(BTD)-N-heterocycle derivatives by metal-catalyzed cross-coupling reactions with relatively good yields. The photophysical characteristics of these derivatives were assessed in solution through UV-vis absorption and steady-state fluorescence emission spectroscopies. These compounds show absorption maxima in the violet to blue region, related to spin and symmetry-allowed 1 π → π* electronic transitions. The BTDs display fluorescence in the visible region of the electromagnetic spectrum, depending on their chemical structure and solvent, ranging from 499 to 570 nm. It was demonstrated that both ground and excited states are influenced by the substituents in the BTD core. In addition, a proof of concept was presented using these compounds as sensors for water in an organic environment. Theoretical calculations data provided a comprehensive insight into the structural and electronic factors that govern the photophysical behavior of these compounds. Solvent-induced twists result in a blueshift in the UV-vis spectra. The molecular electrostatic potential (MEP) provides insights into interactions, revealing that the addition of water influences both emission and molecular structure. The study reported herein describes the synthesis of benzothiadiazole (BTD)-N-heterocycle derivatives by metal-catalyzed cross-coupling reactions with relatively good yields.