Multi-functional benzothiazole-based phenothiazine derivatives: mechanochromism, acidochromism, and anticounterfeiting application

Abstract

The development of stimuli responsive materials has advanced rapidly owing to their fascinating colour switching properties and wide range of applications in optoelectronics. In this contribution, we have designed and synthesized four benzothiazole-based phenothiazine derivatives PTZH, PTZCHO, PTZCN, and PTZBT with different electron withdrawing groups by the Suzuki cross-coupling reaction. The solvatochromism, luminescence behavior of the aggregates, mechanochromism, acidochromism and anticounterfeiting applications have been explored. The compounds PTZH and PTZCHO exhibit strong fluorescence at higher water fraction as a result of nanoaggregate formation, which is confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Among all the compounds, compound PTZH exhibited the highest quantum yield of 66% in dioxane and the longest fluorescence lifetime of 4.08 ns in dichloromethane. All the compounds (PTZH, PTZCHO, PTZCN, and PTZBT) are highly emissive in their solid-state, and exhibit bathochromic shift in the emission wavelength in response to external mechanical grinding. The PXRD analysis reveals the transformation from more crystalline to less crystalline, which accounts for the mechanochromic behavior. These compounds exhibit rapid and reversible solid state acid base responsiveness, demonstrating the potential for sensor applications. The compound PTZH owing to its strong fluorescence and high thermal stability shows potential for anticounterfeiting applications.