Small Electron-Rich Isomeric Solid-State Emitters with Variation in Coplanarity and Molecular Packings: Rapid and Ultralow Recognition of TNT

Abstract

Fast, on-the-spot detection of TNT (2,4,6-trinitrotoluene) in ultralow concentration is in high demand to prevent illegal transport and find explosive formulations before and after the explosion. This work demonstrates an optoelectronic strategy to identify TNT selectively in solution, solid, and vapor phases by rapid fluorescence (FL) quenching as low as 15.24 parts per quadrillion (ppq) level using a couple of easily accessible, structurally diverse positional isomeric electron-rich solid-state emitters as promising small molecules. These solid-state emitters display superior sensitivity in comparison to many reported polymeric materials. The aggregates (almost aqueous solution) of these probes could detect TNT with a detection limit of 39–65 nM. Our mechanistic investigations using steady-state and lifetime FL studies reveal that the quenching effect in the ground state is practically negligible. Still, the probes’ associated frontier molecular orbitals energy levels favor the photoinduced electron transfer process selectively with TNT. We establish the role of relatively planar molecules for the inclination to the quenching process than the twisted ones. The probes were drop-cast or dispersed on a simple filter paper and employed successfully for onsite TNT detection. The impregnation of these probes on a well-known polymeric platform could also realize a safer detection even during the rainy season. A rapid quenching efficiency of yellowish-green emission is beneficial while treating TNT-mixed soil (0.2 mg of TNT in 2 g of soil) with the probe’s aggregated 90% aqueous solution. Ample crystal void space, available interlayer distances, and suitable orbitals energy gap cooperatively result in a rapid ppq level detection of TNT even in the solid state.

Enhanced TNT vapor sensing through a PMMA-mediated AIPE-active monocyclometalated iridium(iii) complex: a leap towards real-time monitoring

“…The detailed synthetic procedures for ligands and complexes are described in the Experimental section. The complexes were obtained with good yields (>70%) and were characterized by 1 H, 13 C, 31…”

“…24 In the quest to detect nitro-based explosive compounds, various luminescent explosive sensors have been developed, leveraging small molecules, conjugated polymers, self-assembled organic nanomaterials, and metal-organic frameworks. 13,14,[25][26][27][28][29][30][31][32][33][34] These have been evaluated for their utility in both solution and vaporphase sensing, but very few reports for fluorescence-based molecules have been employed to detect TNT vapor. 14,19,25,[34][35][36] Mothika and co-workers reported films of tetraphenylene ethylene-based conjugated microporous polymers (PTPETCz) through an electro-polymerization method using tetra(carbazolylphenyl)ethylene monomer, which can detect TNT vapor even at a very low concentration of 33 ppb.…”

Fluorescent Probes for Detection of Environmental Contaminants (NACs & VOCs): Probe Design from a Supramolecular Perspective

“…Chakravarty et al developed isomeric trimethoxybenzene (TMB)-anchored carbazole (CBZ) linked unsymmetrical anthracenyl π-conjugated solid-state emitters (Probe 4A and 4B) to detect TNT selectively as low as 15.24 parts per quadrillion (ppq) level (Figure 9a). [63] These two isomers exchanged the position between TMB and CBZ to afford a more planar system Probe 4B, mostly generated by hydrogen bonding (Figure 9b).…”

Concentration-Guided Visual Detection of Multiphase Aliphatic Biogenic Amines through Amine–Phenol Recognition Using a Dual-State Emitter

“…Earlier investigation on emission tuning directed by phenol–amine interactions in solution was inadequate. , Still, biogenic amine–phenol interactions resulting in FL switching for multiphase recognition of selective aliphatic BAs in ultralow concentration are hitherto unexplored. Moreover, purely organophosphonate-based dual-state emitters are considerably rare. , Typically, we deliver multiple solid-state emitters via Horner–Wadsworth–Emmons reactions with suitable phosphonates as precursors. − In contrast, the precursor phosphonate molecule itself is designed to emit in both solution and the solid state strongly and offers a unique approach to detect BAs selectively at an ultralow concentration in the liquid and concentration-controlled detection of BAs (especially 1,3-diaminopropane, 1,3-DAP) in the vapor phase. Primarily, 1,3-DAP (itself not a biogenic amine but considered an analog of BAs) is formed by the oxidation of spermidine and spermine, a crucial BA responsible for diverse physiological processes, including cellular metabolism in all eukaryotic cells …”