Fluorescence quenching aptitude of carbazole for the detection of nitro-aromatics: a comprehensive experimental analysis and computational studies validation

Abstract

Fluorescence quenching studies of carbazole with nitroaromatics were studied and compared with 2-phenyl-1H-phenanthro[9,10-d]imidazole (M1). Carbazole (CBz) can sense all nitroaromatics, in particular picric acid (PA), whereas M1 responds to the ones having acidic hydrogen. The complex formation constant (K_S) and limit of detection (LOD) were measured using the Stern–Volmer plot. Time-resolved fluorescence measurements reveal that quenching is static. We show that the mechanism of quenching involves ground state complex formation. The CBz-PA complex formation involves hydrogen bonding interaction between the N–H group of CBz and nitro group of PA, whereas M1-PA involves proton transfer from hydroxyl group of PA to nitrogen of imidazole in M1. The crystal structure of the ground-state complex (CBz-PA), its topology, and Hirshfeld surface analysis are also presented. Combined experimental and quantum chemical studies and wave function analysis were performed to study the non-covalent interactions and their role in charge transfer (CT) in the CBz-PA complex.