Enhancement of Fluorescence Emission Intensity in a Sulfonyl Hydrazide Derivative of tri(biphenyl‐4‐yl)amine via Solid‐state Grinding with Various Metal Salts: Combined Experimental and Computational Studies

Abstract

AbstractSolid‐state fluorescent materials are in huge demand owing to their potential applications in sensors, imaging, and LEDs. The molecular aggregations in the solid state limit their usage in practical applications. Typically, J‐aggregates show enhanced emission, while H‐aggregates show quenching in the solid state. Few supramolecular approaches (like creating hydrogen bonds) were developed to disturb the π–π and other supramolecular interactions in solid‐state H‐aggregates. Herein, we are reporting a p‐toulenesulfonyl hydrazide derivative of tri(biphenyl‐4‐yl)amine (TBA‐THZ) in the solid state showed negligible emission while grinding with M+X− (M+=alkali and alkali earth metal) salts showed enhanced emission. Existing supramolecular interactions were disturbed by dipole‐ion interactions between S=O⋅⋅⋅M+. The micro/nanometer‐sized salt crystal particles serve as templates for the TBA‐THZ molecules, and in the broad sense, the salt crystal surfaces act as a “solid‐state solvent.” The TBA‐THZ ground with various metal salts showed varied emission intensities; the BaCl2 ⋅ 2H2O salt ground sample exhibited the maximum emission intensity. The KPF6+18‐Crown‐6 sample showed 84 times enhanced emission than the pristine TBA‐THZ. The role of 18‐crown‐6 ether was observed as a donor type for K+ ions. The expected S=O⋅⋅⋅K+ dipole‐ion interactions were elucidated through FT‐IR and computational modelling. The slight change in emission wavelength to the higher side after grinding with metal salt indicates that dipole‐ion interactions might slightly modify the chromophore's electronic structure, encouraging radiative decay and higher emission intensity. In contrast, a similar molecule, TBA‐PH, with no sulfonyl functional group, was silent in emission intensity. The TBA‐PH solid has no significant emission even after grinding with metal salts. The emission capacity of the TBA‐THZ salt‐ground powder remained unchanged at higher temperatures and in a highly humid environment. The fluorescent active salt ground matrix of the TBA‐THZ responded admirably to HCl acid fumes and was regenerated upon exposure to ammonia vapours.