Modulation of the electronic structure and sensing performance toward nitroaromatic explosives of aza-BODIPY derivatives through substituent effect

Selected as fluorescent based chemosensor against nitroaromatic explosives, a series of aza-BODIPYs bearing hydroxyl, bromo, and formyl functions, have been synthesized and evaluated for the underlying interactions involved in their fluorescence quenching mechanisms. As a result, functional groups incorporated into the structure significantly affected the photophysical behaviour and the sensing capabilities of the aza-BODIPY moiety. In the context of the study, K_sv (Stern-Volmer Constant) and QE (Quenching Efficiency) values were evaluated and according to the results, K_sv values obtained between 10⁴ to 10⁶ (up to 10⁶ for hydroxyl bearing aza-BODIPY, 10⁴ for formyl bearing aza-BODIPY, 10⁵ for bromo bearing aza-BODIPY), Moreover, although hydroxyl group, shows the highest K_sv and QE value, it has the less selectivity towards NAC's (Nitroaromatic Compounds) due to its hydrogen bonding and electrostatic interaction capabilities towards nonaromatic nitro compounds. To illuminate the underlying mechanism, theoretical studies and life-time analysis were conducted, interestingly secondary/tertiary excited states were seen, and dynamic quenching was shown as a major difference from tetraphenyl conjugated aza-BODIPY. The change of static quenching to dynamic in all modified aza-BODIPY derivatives highlights the critical role of electronic structure in determining the dominant quenching pathway. With enhanced K_SV and QE values and new mechanistic insights, these findings not only establish aza-BODIPYs as a reproducible platform for nitroaromatic explosive detection with competitive sensing performance, but also effectively show that, with functional group modifications, sensing properties and pathways can be modulated.