How explosive TNP interacts with a small tritopic receptor: a combined crystallographic and thermodynamic approach

Abstract

Herein, the interaction of explosive and pollutant nitroaromatics (epNACs) like 2,4,6-trinitrophenol (TNP) with a small molecular probe has been explored by X-ray crystallography and thermodynamics of the crystallization. The supramolecular host with an unusual crystal packing has been used for the detection of TNP. Fluorescence quenching through the RET–PET–ICT–ACQ mechanism results in a strong pi–pi interaction between the receptor and TNP. Both simulated and experimental FTIR spectroscopies have been performed to investigate the sensing event from solid phase perspective. The enhancement in enthalpy (ΔH) of the host–guest adduct suggests an endothermic reaction suitable for sensing a heat-sensitive explosive like the TNP molecule. On the other hand, entropy (ΔS) enhancement in the crystal formation suggests trapping or releasing of the solvent molecule. In reality, it is noticed from the SCXRD study that acetonitrile undergoes co-crystallization in the host–guest adduct. Ultimate energy (E_final = E_adduct − E_precursor) of adduct is lowered up to −919.89 Hartree, which favors the crystallization. The recognition event is highly selective for TNP, Cu²⁺, and F⁻ among the other analytes, where TNP shows fluorescence turn-off and Cu²⁺ and F⁻ show turn-on response at different spectroscopic energy levels. Indeed, the receptor proves to be a novel tritopic receptor for selective detection of cation, anion, and neutral analytes with a distinguishable signal. In real time stepping, chromatographic strips have been designed for on-spot chromogenic and fluorogenic detection of the TNP-like explosive molecule for homeland safety.