Zhengfeng Xie

A new highly selective fluorescent turn-on chemosensor for cyanide anion

A new simple molecule, 2-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)malononitrile (M1), was synthesized successfully by the Knoevenagel condensation reaction between 2-phenyl-1,2,3-triazole-4-carboxaldehyde and malononitrile. The receptor M1 is highly sensitive and selective to cyanide anion due to the nucleophilic addition of cyanide anion with M1. Distinct changes on UV-vis and fluorescence spectra can be detected with the addition of cyanide anion to the DMSO solution of M1. Optical properties of M1 were scarcely affected by the addition of other common background anions (F(-), Cl(-), Br(-), I(-), SCN(-), OH(-), CO4(2-), H2PO4(-), SO4(2-), HSO4(-), AcO(-), and NO3(-)) under the same condition. The detection limit of CN(-) reaches ~1.43 μM by M1 and the presence of background anions brought very slight interference for the detection of CN(-).

A highly selective and sensitive acylhydrazone-based turn-on optical sensor for Al3+

An acylhydrazone-based chemosensor M1 (2-hydroxy-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)benzohydrazide) was synthesized for the detection of Al3+. Unlike other receptors reported, M1 showed an excellent selectivity which could hardly be interfered by other ions like Cu2+ and Fe3+. The fluorescence intensity varied almost linearly vs. the concentration of Al3+, and the detection limit of Al3+ was estimated to be 1.2 × 10−8 M, illustrating that M1 can be used as a “turn-on” fluorescent chemosensor to selectively and sensitively detect Al3+ in ethanol.

Barbituric acid–triphenylamine adduct as an AIEE-type molecule and optical probe for mercury(II)

A type of simple-structured triphenylamine–barbituric acid adduct, M1, has been synthesized using a practical and simple Knoevenagel reaction under mild conditions. M1 displayed interesting aggregation-induced emission enhancement (AIEE) characteristics in a THF (good solvent)–water (poor solvent) system. The fluorescence intensity of M1 increased significantly when the water fraction in the co-solvent system surpassed 70%, and the emission maxima shifted from ∼568 nm (in THF) to ∼610 nm (in THF/water = 1 : 19, v/v). By taking advantage of the specific binding of the thymine-like amide groups in M1 with Hg2+, the fluorescence of M1 was enhanced to realize the successful turn-on detection of Hg2+ in an aqueous environment (THF/water = 3 : 7, v/v). Hg2+-induced aggregation of M1 is a plausible reason for the probing process.

PMoA/MCM-41 catalyzed aza-Michael reaction: special effects of mesoporous nanoreactor on chemical equilibrium and reaction rate through surface energy transformation

PMoA/MCM-41, a heterogeneous catalyst, acts as a nanoreactor to catalyze the aza-Michael reaction of nitro-olefins with hydrazides. Experimentation showed that this mesoporous nanoreactor could affect chemical equilibrium and kinetics. The possible mechanisms were thoroughly studied, and the surface energy of PMoA/MCM-41 was demonstrated to promote the aza-Michael reaction.

Oxidation of aldehydes to carboxylic acids in water catalyzed by cobalt(II) Schiff-base complex anchored to SBA-15/MCM-41

Cobalt(II) Schiff-base complexes were successfully anchored to SBA-15/MCM-41 and used as a catalyst for the oxidation of aldehydes to afford carboxylic acids in water under the action of hydrogen peroxide. Reaction conditions, such as different catalyst type, reaction temperature, reaction time, solvents media, and catalyst amount were studied systematically. High yield (up to 98%) of the process was reached. Such substrate-supported catalyst can be reused up to five times without significant loss of its catalytic activity which is not lower than 85%.

Aqueous nanodispersion of acetylene tethered, quinoxaline-containing conjugated polymer as fluorescence probe for Ag+

A type of carbazole-based, quinoxaline-containing conjugated polymer with tethered acetylene groups, P-2, was successfully synthesized through the desilylation of triisopropylsilyl (TIPS) protected precursor polymer. A nanodispersion of P-2 in water was prepared by reprecipitation treatment and displays acceptable quantum efficiency (QE, 0.20). Optical properties of P-2 in THF solution and nanodispersion state were characterized by UV-vis and photoluminescence (PL) analyses. Specific binding with Ag+ of P-2 was validated by UV-vis and PL analyses against other metal ions. The corresponding results suggest that P-2 possesses selectivity and sensitivity toward Ag+. Around 82% of the PL intensity of P-2 was quenched when the concentration of Ag+ in the probing mixture reached ∼5.1 × 10−4 M. The detection limit for Ag+ was evaluated as ∼64 nM (S/N = 3). The synergic effect of the tethered acetylenes and N atoms in the quinoxaline segments interacting with Ag+ is the possible reason for the specific response of P-2 for Ag+.

An aggregation-induced emission enhancement fluorescent benzoxazine-derived macromolecule: catalyst-free synthesis and its preliminary application for the determination of aqueous picric acid

A tetraphenylethene-containing fluorescent macromolecular benzoxazine derivative (TPE-BOZ) was synthesized via the Mannich reaction under catalyst-free conditions using 4,4′-(1,2-diphenylethene-1,2-diyl)diphenol, poly(propylene glycol)-bis-(2-aminopropylether) and formaldehyde as the starting materials. TPE-BOZ displayed typical aggregation-induced emission enhancement characteristics in ethanol (a good solvent) and water (a poor solvent), which stemmed from the incorporation of tetraphenylethene moieties into its structure. The fluorescence of TPE-BOZ in a high water fraction medium (ethanol : water 1 : 9 v/v) was effectively quenched by the introduction of picric acid with a Stern–Volmer value (ksv) of 1.134 × 107 M−1. The detection limit for picric acid by TPE-BOZ was 4.47 nM. The presence of other common nitrocompounds and solvent residuals did not significantly interfere with the recognition of picric acid by TPE-BOZ. TPE-BOZ can also be used as a solid-state probe to determine picric acid.

N-Unsubstituted-1,2,3-triazole-tethered, AIEE type conjugated polymer as a ratiometric fluorescence probe for silver ions

A type of N-unsubstituted-1,2,3-triazole-decorated conjugated polymer (P3), with the feature of aggregation-induced emission enhancement (AIEE), was successfully synthesized via a Cu+-catalyzed click reaction between an acetylene-substituted precursor polymer (P2) and azidotrimethylsilane. Except for Ag+, the introduction of other metal ions had only a slight influence on the optical properties of P3. With the introduction of aqueous Ag+, the fluorescence of P3 in a THF–water mixture (vTHF/vwater = 4/1) (buffered with Tris–CA, 1 mM, pH = 7.4) displayed a ratiometric alteration at the blue (∼420 nm) and green (∼495 nm) bands. The corresponding I495/I420 ratio values maintained an upward trend throughout the titration process of Ag+. The detection limit of Ag+ reaches ∼1.4 μM (3σ/k), as evaluated from the corresponding relationship between I495/I420 and [Ag+]. The aggregation between the polymer chains induced by a Ag+–triazole interrelation is the plausible reason for the alteration of P3s optical properties.