Selective sensing of cyanide ions: impact of molecular design and assembly on the response of π-conjugated acylhydrazone compounds

This study investigates the sensing properties of two distinct compounds, denoted as 1 and 2, featuring acylhydrazone units. Spectroscopic analyses reveal the disruption of the supramolecular assembly upon binding with cyanide ions, consequently due to the hydrogen bonding interaction with acylhydrazone units. This leads to a ratiometric, color-changing response of both the compounds specifically towards cyanide ions. The investigation sheds light on the reversible nature of the cyanide-probe interaction and highlights the potential for reusability in cyanide ion detection. Moreover, compound 1, distinguished by its long alkyl chains, displays a superior response to CN- ions (∼4-fold larger signal), in contrast to compound 2. However, interference was observed from other basic anions, such as F- and AcO-. The research suggests the dominating role of supramolecular assembly, intermolecular interaction, and local hydrophobic environment around the binding sites on the analytical performance of the probe molecules. The findings underscore the significance of structural design and molecular assembly in dictating the selectivity and sensitivity of compounds, offering valuable insights for the development of efficient sensor systems in diverse real-world applications.

A novel bifunctional-group salamo-like multi-purpose dye probe based on ESIPT and RAHB effect: Distinction of cyanide and hydrazine through optical signal differential protocol

A novel bifunctional-group multi-purpose dye probe p-TNS has been designed and synthesized. The probe p-TNS has unique excited-state intramolecular proton transfer (ESIPT) and resonance-assisted hydrogen bonding (RAHB) coupled system, was confirmed to detect cyanide and hydrazine by blocking the ESIPT effect. Cyanide can change the fluorescence of the solution from bright green to orange-red (116 nm Stokes shift), while hydrazine causes the bright green fluorescence to be quenched. The recognition mechanism of the probe p-TNS to CN^- and N₂H₄ was proposed reasonably through spectral characterizations and theoretical calculations. Combined with theoretical calculations, it was speculated that the solvent dependence may be caused by the ICT effect in the molecule. The probe p-TNS could be prepared into test strips for the detection of cyanide and hydrazine. In addition, the probe molecule can also be used to detect trace amounts of cyanide in agricultural products, and respond to gaseous hydrazine by direct contact, indicating that the probe p-TNS has good practical application prospects. Therefore, this molecular framework provides a new way of thinking about detecting multiple target substances.

Nickel(II) monobenzoporphyrins and chlorins: synthesis, electrochemistry and anion sensing properties

A series of nickel(II) monobenzochlorins (MBCs) and monobenzoporphyrins (MBPs) containing β-appended or meso,β-fused indanedione (IND) or malononitrile (MN) groups were synthesized and characterized for their physicochemical, electrochemical and anion sensing properties. Each investigated compound contained four meso-phenyl rings and a single β,β'-fused 4,5-di(methoxycarbonyl)benzene ring, with the chlorins represented as NiMBC(Y)₂(R)₄ and the porphyrins as NiMBP(Y^F)₂, where Y is an indanedione (IND) or malononitrile (MN) group, R = H or Br and Y^F is a meso,β-fused IND or MN substituent. One of the investigated compounds, NiMBP(IND)₂, was structurally characterized and shown to possess a ruffled macrocyclic conformation. The monobenzochlorins, NiMBC(IND)₂, NiMBC(IND)₂Br₄ and NiMBC(MN)₂, reversibly respond to basic anions such as CN^-, F^-, OAc^- and H₂PO₄^- through a visible color change assigned to the deprotonation of the vicinal proton on the appended IND or MN substituents. The malononitrile-fused Ni^II monobenzoporphyrin, NiMBP(MN)₂, exhibited a selective but irreversible visual detection of cyanide ions (LOD = 2.23 ppm). This reaction afforded a tri-fused π-extended monobenzoporphyrin product represented as NiMBP(VCN)₂ (where VCN = meso,β-fused vinyl cyanide) in non-aqueous media and proceeded via anion induced electron transfer (AIET). The in situ generated π-extended porphyrin was also isolated and characterized as to its physicochemical and electrochemical properties and found to possess a narrow electrochemical HOMO-LUMO gap of 1.46 V along with a near-IR (NIR) absorption band located at 861 nm.

Two novel tetraphenylethylene-skeleton salamo-type fluorescent probes: specific recognition of cyanide through different response patterns

The possible sensing mechanism of probes TPES1 and TPES2 towards CN− ions.

Highly sensitive turn-off fluorescent detection of cyanide in aqueous medium using dicyanovinyl-substituted phenanthridine fluorophore

Herein, the turn-off fluorescence sensor of 2-((4'-(7,8,13,14-tetrahydrodibenzo[a,i]phenanthridin-5-yl)-[1,1'-biphenyl]-4-yl)methylene)malanonitrile (7) was developed for the recognition of CN- ions and studied using different spectroscopic techniques. The selective recognition of CN- ions by 7 was investigated via UV-vis spectroscopy and fluorescence studies in acetonitrile solvent, which exhibited an obvious color change from orange to colorless under 365 UV light. The sensor compound 7 possesses a high binding constant (K a) for CN- ions in the order of 5.22 × 106 M-1. The results from the interference studies revealed that probe 7 shows high sensing selectivity and sensitivity for CN- ions over other competitive anions. Probe 7 interacts with cyanide to form a 1 : 1 adduct, and this mechanism was further verified by 1H NMR titration, Job's plot analyses and DFT studies. The sensor probe 7 exhibits advantages such as low limit of detection (LOD) of 39.3 nM, fast response and sensing in a wide pH range of 3 to 11. The practical application of 7 was successfully demonstrated for the determination of CN- ions in test paper strips and various water samples.

A new salamo-based colorimetric and fluorescent turn-on sensor with aggregation-induced emission for the rapid and highly sensitive detection of cyanide in real samples

A new, simple, and easy-to-manufacture highly selective and sensitive dual-mode sensor A1 with the aggregation-induced emission properties is used for CN⁻ colorimetric and fluorescence detection.