A highly emissive Zn(II)-pyridyl-benzimidazolyl-phenolato-based chemosensor: detection of H2PO4-via "use" and "throw" device fabrication.

2-Ethoxy-6-[1-(phenyl-pyridin-2-yl-methyl)-1H-benzoimidazol-2-yl]-phenol (HL) selectively serves as a sensitive ‘turn on’ Zn2+ sensor in 9 : 1 (v/v) DMSO/H2O (HEPES buffer, pH = 7.4) medium in the presence of sixteen other cations at the limit of detection (LOD) of 3.2 nM. The strong blue emission of the complex, {[Zn(L1)OAc]} (HL1 = benzimidazolyl ring-opening structure of HL) (λem, 461 nm), is quenched by H2PO4− in the presence of eighteen other anions and the LOD is 0.238 μM. The emission of the complex is due to restricted intramolecular rotation (RIR) followed by chelation-enhanced fluorescence (CHEF). The quenching of the emission of [Zn(L1)OAc] by H2PO4− (in the presence of other PVs (inorganic and biological) as well as additional anions) is due to the ‘turn off’ fluorescence via the demetallation and release of the nonfluorescent ligand, HL, and [Zn(H2PO4)]+. An INHIBIT logic gate memory circuit of the probe HL was devised with Zn2+ and H2PO4− as two consecutive inputs. The percentage of H2PO4− recovery was excellent and was obtained from distilled, tap, and drinking water sources. The bright blue emission of [Zn(L1)OAc] further triggered the fabrication of ready-made portable thin films of the Zn-complex, which executed a cost-effective ‘on-site’ solid-state contact mode detection of H2PO4− with selectivity at the picogram level (10.97 pg cm−2) by monitoring the intensities of quenched spots under UV light upon varying the analyte concentration from 10−8 to 10−3 M. Finally, taking advantage of reversible fluorescence switching, a simple and definite ion-responsive security feature was successfully embedded into a “use” and “throw” solution-coated paper strip of the Zn(II)-pyridyl-benzimidazolyl-phenolato-based chemosensor, which efficiently detected H2PO4− in water by a successive ‘ON–OFF’ fluorescence switching-driven security activity without any exhaustion of the emission phenomenon.