An Efficient Fluorescent Probe Based on Triphenylimidazole End‐Capped Diketopyrrolopyrrole for Selective Detection of CN ⁻ and TFA Through <i>On–Off–On</i> Response

A triphenyl-imidazole end-capped donor-acceptor type potential molecular probe 3 has been designed and synthesized. Probe 3 upon interaction with different classes of metal ions/anions and NPPs displayed high selectivity with CN^- anion (LOD = 20.42 nM) through fluorescence "turn-Off" response and a naked-eye sensitive visible color change. Job's plot analysis revealed a 1:2 binding stoichiometry. The interaction of 3.CN^- with trifluoroacetic acid (TFA) showed reversible behavior wherein the intensity of the probe rejuvenated, fluorescence "turn On-Off-On response," along with a change in color of the medium. The change in rate constants and fluorescence lifetime of the probe suggested that the interaction of probe with CN^- occurred in two steps: H-binding and deprotonation of -NH functions of imidazolyl units. The mode of binding of probe with CN^- was confirmed by ¹H NMR, FTIR, and HRMS data. The potential application of molecular probe has been examined to detect the CN^-, TFA, and TFA vapor on test paper strips. The smartphone-based RGB analysis of paper strips also supported on-site colorimetric detection of CN^-. Probe shows good recovery percentage of CN^- in real water sample analysis. The output emission using chemical inputs CN^- and TFA mimics the function of an IMP logic gate.