Detection of small molecular toxins using azacalix[4]arene architecture and its theoretical investigations

[Display omitted] •Design and synthesis of an azacalix[4]arene based architecture (BNAC).•Selective recognition of N-methyl-4-nitroaniline and monocrotophos.•Sensing of both the analytes up to sub micromolar concentration.•Theoretical studies insight about host–guest interactions and binding phenomena. We demonstrate an azacalix[4]arene based bifunctional probe, viz. bisnaphthylated-azacalix[4]arene (BNAC) for the selective recognition of molecular toxins such as monocrotophos (MCP) and N-methyl-4-nitroaniline (MNA). The photophysical properties, especially the emission studies were introduced for monitoring the host–guest complexation. Noteworthy, the emission responses of the host exclusively alter according to the functionalities attached to the guest molecules. For instance, MCP being electron-rich enhances the emission intensity of BNAC upon complexation by donating electrons to the electrophilic sites of the receptor. Inversely, MNA having electron-withdrawing nitro groups readily interacts with the highly conjugated naphthalene rings and suppresses the emission maxima of the receptor through photoinduced electron transfer (PET). Job’s plot reveals both MNA and MCP exhibit 1:1 stoichiometry upon complexation with BNAC. Computational studies including molecular docking and DFT calculations were carried out to predict the binding affinity, plausible host–guest interactions and to investigate the binding mechanism.