Synthesis and photo-electro-thermal characterization of non-symmetrical 4,7-dibromobenzo[c][1,2,5]thiadiazole derivatives

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This work describes the synthesis of new fluorophores based on non-symmetric 4,7-dibromobenzo[c][1,2,5]thiadiazole derivatives with benzene ethynyl tetrazole and propargyl carbazole as terminal groups. The new compounds were obtained using the Sonogashira cross-coupling reaction and produced good yields. The benzothiadiazole derivatives presented absorption in the ultraviolet–visible region (391–400 nm) ascribed to spin and symmetry allowed electronic transitions 1ππ*. The main fluorescence emission located at 460–500 nm was observed with solvatochromism up to 40 nm, indicating higher electronic delocalization in the excited state. Electrochemically, the compounds are electroactive in both the anodic and cathodic potential range. The magnitude of oxidation potentials ranged from 1.54 to 1.61 V vs. NHE and reduction potentials ranged from −2.00 to −2.05 V vs. NHE. The HOMO and LUMO energies were calculated using cyclic voltammetry data. HOMO energies ranged from −6.16 to −6.23 eV and EA energies ranged from −2.57 to −2.62 eV, and thus, the electrochemical band gap of compounds ranged from 3.56 to 3.66 eV. Thermogravimetric analysis showed that the compounds presented good thermal stability up to 200 °C. The DFT and TD-DFT calculations were performed at the B3LYP/6-31G level of theory. The results show that the dipole moment of the molecules varies tremendously from the electronic ground to excited state, ensuring a charge transfer character.