Dithiafulvenyl-substituted triazolobenzothiadiazines as a new family of multifunctional chromophores

Abstract

This work investigates a new class of organic π-chromophores which contain an electron-donating 1,4-dithiafulvenyl group in conjugation with an electron-withdrawing 8H-benzo[e][1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-8-one core in their molecular structures. The synthesis of these compounds used a phosphite-promoted olefination reaction as a key step, through which 1,3-dithiole-2-thione was reacted with corresponding benzotriazolothiadiazinone counterparts to form a flat polycyclic π-framework, allowing electron push–pull effects to occur. The resulting donor–acceptor chromophores were found to exhibit significant intramolecular charge-transfer (ICT) properties, giving strong absorption in the visible region of the spectrum. The triazolyl unit in these molecules can be protonated by strong acids to show enhanced ICT effects, while electrochemical analysis revealed that these compounds possess amphoteric behavior with tunable band gaps (ca. 1.3–1.4 eV) and are potentially useful organic semiconductors. We also demonstrated that this type of chromophore can be readily functionalized on the surface of TiO₂ nanoparticles without losing absorption performance. Finally, the dithiafulvenyl group incorporated in the molecular structure was found to enhance antibacterial activity, rendering the chromophores potential candidates for antibacterial/antimicrobial coatings.