Photophysical and anion sensing properties of a triphenylamine-dioxaborinine trimeric compound

Herein, we report the synthesis and photophysical characterization of the novel tris(4-(2,2-difluoro-6-methyl-2H-1λ³,3,2λ⁴-dioxaborinin-4-yl)phenyl)amine trimeric probe (A2) via the reaction between triphenylamine (1), acetic anhydride, and BF₃·OEt₂ implying the twelve new bond formation in a one-pot manner. This highly fluorescent compound in solution (φ up to 0.91 at 572 nm) and solid state (φ = 0.24 at 571 nm) showed a better solvatofluorochromism than its analog monomeric A1 due to symmetry-broken charge transfer, which is consistent with high solvent dipolarity (SdP) response in Catalán's multiparametric regression. Notably, A2 had a high sensibility and selectivity for CN^- or F^- in solution (LODCN^-/F^- = 0.18/0.70 μM), and CN^- can be discriminated from F^- by the reaction of A2 with 3.0 equiv. of CN^-. In addition, A2 was impregnated on filter paper to prepare test strips that were applied to naked-eye qualitative sensing of CN^- or F^-. Finally, the octupolar system in A2 allows for better action of two-photon excitation cross-section values when compared with that of the dipolar structure in A1. These findings provide further information for the design of new efficient two-photon absorption dyes.

Nucleophilic Approach to Cyanide Sensing by Chemosensors

Cyanide anion has wide use in industrial areas; however, it has a high toxic effect on the environment as waste. Moreover, plant seeds contain cyanide that is often consumed by human beings. Therefore, many studies are carried out to determine cyanide. Especially, optical sensors showing colorimetric and fluorimetric changes have been of considerable interest due to their easy, cheap, and fast responses. This review discusses recent developments in the colorimetric and fluorimetric detection of cyanide by nucleophilic addition to different types of receptors via the chemodosimeter approach. The sensitivity and selectivity of the sensors have been reviewed for changes in absorption and fluorescence, naked-eye detection, real sample application, and detection limits when interacting with cyanide.

Triphenylamine-based small-molecule fluorescent probes

Ammonia with the three hydrogens substituted by phenyls is known as triphenylamine (TPA), and is one of the most useful compounds because of its vast practical applications. Chemists have produced thousands of TPA derivatives to date. Because of its biocompatibility and structural features, it has been widely used in the fields of molecular recognition, molecular imaging, materials chemistry, and also in biology and medical science. Its strong electron-donating ability encourages scientists to produce different types of probes for molecular recognition. This review is based on recent developments and advances in TPA-based small molecular fluorescent probes within the time period 2010-2021. This extensive review may expedite improvements in more advanced fluorescent probes for vast and stimulating applications in the future.

"Turn-on" unsymmetrical azine based fluorophore for the selective detection of diethylchlorophosphate via photoinduced electron transfer to intramolecular charge transfer pathway

The detection of chemical warfare agents (CWAs) in a highly selective, sensitive and speedy manner is essential for public safety in the case of terrorist attacks and achieving this is a challenging task. This study involves in developing a new unsymmetrical azine based fluorophore 4-((E)-(((E)-2-methoxybenzylidene)hydrazono)methyl)benzonitrile[A1] which shows high selectivity and sensitivity to the nerve agent mimic molecule, diethylchlorophosphate (DCP) through fluorescence switch on mechanism. In a fascinating manner, DCP sensing by A1 operates via solvent dependent optical output mechanisms. In the absence of DCP, the fluorescence of A1 was in the off state through photoinduced electron transfer process. In the presence of DCP, a nucleophilic substitution reaction occurs at the imine nitrogen is closer to the anisole moiety that results in the formation of a new intramolecular charge transfer state along with fluorescence enhancement. In acetonitrile, A1 shows 1763-fold fluorescence enhancement in the presence of DCP with a detection limit of 9.86 nM. In Acetonitrile/water (2:8) mixture, protonation at the imine nitrogen leads to 1188-fold fluorescence enhancement. The sensing mechanisms are confirmed by both experimental and time dependent density functional theoretical studies.

Bisphenol-based cyanide sensing: Selectivity, reversibility, facile synthesis, bilateral "OFF-ON" fluorescence, C2ν structural and conformational analysis

A structurally characterized novel dual-pocketed tetra-conjugated bisphenol-based chromophore (fluorescence = 652 nm) was synthesized in gram scale in ~90% yield from its tetraaldehyde. Highly selective, naked-eye detection of CN^- (DMSO/H₂O) was confirmed by interferent testing. A detection limit of 0.38 µM, within the permissible limit of CN^- concentration in drinking water was achieved as mandated by WHO. The "reversibility" study shows potential applicability and reusability of Sen. Moreover, cost-effective and on-site interfaces, application tools such as fabricated cotton swabs, plastic Petri dishes, and filter papers further demonstrated the specific selectivity of Sen for the toxic CN^-. In addition, an easily available and handy smartphone-assisted "Color Picker" app was utilized to help estimate the concentration of CN^- ion present. A dual phenol deprotonation mechanism is active and supported by ¹H NMR spectroscopic data and DFT calculation results.

Turn-on fluorescent naphthalimide-benzothiazole probe for cyanide detection and its two-mode aggregation-induced emission behavior

Naphthalimide-benzothiazole conjugate (NBTZ) linked by cinnamonitrile was designed, synthesized, and fully characterized by NMR (¹H, ¹³C, DEPT, HSQC) and high-resolution mass spectrometry. NBTZ exhibited unique turn-on fluorescence in the presence of CN^- with relatively high selectivity compared to other anions such as SCN^-, HSO₄^-, ClO₄^-, NO₃^-, Cl^-, Br^-, I^-, and PO₄^-3 in tetrahydrofuran (THF). The detection limit for CN^- was found to be 3.35 × 10^-8 M in THF. The sensing mechanism was analyzed through ¹H, ¹³C, DEPT, and mass spectroscopy. NBTZ also showed two-mode aggregation-induced emission (AIE) in THF-H₂O mixtures. In a 30:70 THF-H₂O (v/v) mixture, the maximum AIE was observed at 430 nm (blue) because of the rotation of the CC bond between the naphthalimide ring and the phenyl ring was restricted. In 10:90 THF-H₂O (v/v), a new red-shifted AIE appeared at 490 nm (cyan), due to the extended π-conjugation induced by restriction of rotation of the CC bond between the benzothiazole and naphthalimide rings.

D-π-A azine based AIEgen with solvent dependent response towards a nerve agent

We developed a D-π-A based unsymmetrical azine molecule 4-((E)-((E)-(4-(dipropylamino)benzylidene)hydrazono)methyl)benzonitrile [DPBN] and studied its optical and aggregation induced emission properties. The DPBN molecule shows good aggregation induced emission (AIE) behaviour with 1157-fold fluorescence enhancement in the aggregated state. In addition to that, both colorimetric as well as fluorometric sensing studies revealed that DPBN selectively detects diethylchlorophosphate (DCP), a potent nerve agent. Interestingly, DPBN shows solvent dependent optical output in the presence of DCPvia two different mechanisms. In the monomer state, it shows red shifted fluorescence enhancement along with color change from colorless to orange color via the formation of a new intramolecular charge transfer state in pure tetrahydrofuran (THF). In the aggregated state, DPBN shows blue shifted emission with fluorescence enhancement in THF-water mixture by protonation at the amine nitrogen centre. Thus, DPBN can be used as a diagnostic measure to selectively detect nerve agents like DCP. This study also paves the way for further development of molecular probes for nerve agents that would represent immense implications in various fields of chemistry and biology.

Azine based AIEgens with multi-stimuli response towards picric acid

Selective detection of picric acid using AIEgens via fluorescence enhancement and quenching in the monomer and aggregated from respectively.