•Rational design and assemble of new bimetallic based chemodosimeters.•The Re(I)-Pt(II) complex is a good food detector for volatile biogenic sulfides.•Naked-eye luminescent responses specific to CH3SH and CH3SCH3 by the food detector to check the freshness of meat.•Applicable for in-situ CH3SH monitoring in real rotten pork samples and as efficient as GCMS detection.Detection of volatile biogenic sulfides (VBS) plays a crucial role in food safety because the amounts of these compounds can reflect the freshness of meat. A new indicator-displacement assay with Re(I)-Pt(II) complexes, [Re(Lig)(CO)3(bridge)]–[Pt(DMSO)(Cl)2] (1: Lig = 5-phenyl-1,10-phenanthroline and bridge = NCS−; 2: Lig = 5-phenyl-1,10-phenanthroline and bridge = CN−; 3: Lig = 2,2′-biquinoline and bridge = NCS−), was demonstrated to be a very effective sensing method to VBS. The results indicated that the control of Re(I)–bridge–Pt(II) and Re(I)–ligand combination are able to regulate their sensing selectivity and sensitivity. This system was successfully applied to detect CH3SCH3 in real rotten pork with a linear luminometric response up to 20.0 mg kg−1 (R = 0.997) with the detection limit as 0.05 mg kg−1. Complex 1 also gave comparable results on the detection of VBS with respect to those determined by GCMS with recovery range from 76% to 102% (RSD% = 13.8).

•A product-imprinted polymer based organocatalyst was developed.•The organocatalyst is amphiphilic and photoswitchable.•The catalyst catalyzes aldol reaction with good conversion and low catalyst loading.•The catalyzed aldol reaction performs well in a mixed solvent of DMSO and water.A series of amphiphilic molecularly imprinted polymers (MIP1, MIP2, MIP3, MIP4, MIP5, and MIP6) containing hydrophobic photoresponsive sites and hydrophilic catalytically active sites were fabricated using bifunctional monomers. These polymers were characterized by scanning electron microscopy, N2 adsorption–desorption analysis, Fourier Transform infrared spectroscopy, thermal gravimetric analysis, and ultraviolet–visible spectroscopy. The catalytic activity of the amphiphilic molecularly imprinted polymer was investigated towards the aldol reaction between p-nitroaldehyde and acetone (a molecular enlargement reaction) in a mixed solvent of DMSO and water at room temperature. The polymer catalyst MIP3 performs best, and displayed good conversions with low catalyst loading (5 mol% of l-hydroxyproline with respect to the aldehyde) and photoswitching properties (photo-regulated conversion difference of 20%). Compared with the corresponding non-imprinted polymer, a higher binding capacity, higher conversion, and better photoswitching properties were obtained when the molecularly imprinted polymer was used as the catalyst, illustrating the importance of the specific cavities in the molecularly imprinted polymer.Download full-size image

•Pyridinium-salt-based electrochromic materials, AETPDs, were designed and synthesized.•AETPDs exhibit dual-color and good electrochromic properties.•The carboxylic acids and N-substituents greatly influence their electrochromic properties.This study aims to achieve dual-color properties for pyridinium-salt-based electrochromic materials. A novel series of 4′-(4-alkyl ester)-4,2′:6′,4″-terpyridinium derivatives were designed and synthesized through the introduction of an ester group onto the benzene ring of 2,4-di(4-pyridyl)-4-benzylpyridinium derivatives. Dual-electrochromic devices based on these compounds were fabricated. Multiple shades of green and yellowish green colors were obtained by changing the type of carboxylic acids and the nitrogen substituents. The type of carboxylic acids and the nitrogen substituents significantly influenced their electrochromic properties. 4′-(4-Alkyl ester)-4,2′:6′,4″-terpyridinium derivatives show good electrochromic properties such as high coloration efficiency, reasonable contrast, satisfactory optical memories, and redox stability. The dual-electrochromic materials are promising candidates for applications in electrochromic display systems.Download high-res image (117KB)Download full-size image

Polyvinylchloride (PVC) is a typical non-biodegradable plastic that is resistant to chemicals, sunlight, and weathering. These properties make its disposal problematic, as items made from PVC retain their form for decades. The objective of this study is to provide an effective waste management method for the degradation of huge amounts of the robust plastic waste. In this work, a rapid chemical treatment method has been developed by utilizing the Fenton catalyst to break down PVC plastic wastes into recoverable high-value organic compounds. During this chemical process, surface activation of PVC takes place to generate coordinating sulfonate groups that get tagged with iron(III) chloride. The iron(III)-tagged PVC is a highly active Fenton catalyst that breaks down the entire bulk polymer into a number of valued organic acids selectively using hydrogen peroxide as a green oxidant. By using this procedure, all treated PVC plastic wastes were completely degraded into water soluble organic compounds and CO2 under ambient dark conditions within 10 min. The dissolved organic compounds were identified mainly as mono- and dicarboxylic acids. The formation of these products indicates that the reaction is selective, which is not expected from the classical Fenton-type radical oxidation reactions. A detailed study was conducted to probe the possible mechanism of degradation that takes place during the chemical treatment process. It was found that the temperature conditions for PVC activation significantly affect the number of activated sites (sulfonated groups) generated on the polymer backbone, in which the carbon-to-sulphur atom (C/S) ratio can vary from 8:1 to 29:1. The degradation efficiency, which is typically defined in terms of the bulk mass of the treated PVC plastics, was found to be greater than 98% in all cases. This also included the real samples of rigid PVC pipe. The recovered amount of the characteristic compound butanedioic acid, which is formed during the PVC plastic breakdown process, was found to consistently vary from 9.8% to 61.3% with respect to the C/S ratio. The results of this study are also helpful for the further development of similarly fast and effective plastic waste treatment and management protocols in lieu of landfill disposal, which is particularly important for polymers such as polyethylene (PE), and polypropylene (PP).

•An azobenzene-containing catalyst supported on zirconium phosphonate was synthesized.•The catalyst catalyzes one-pot three-component Mannich reaction in water.•The catalyzed Mannich reaction could be photo-controllable.•The catalyst could be recycled and recovered easily.An environmentally friendly, photocontrollable and highly recyclable catalyst (ZrOPPAZOSO3H) has been synthesized by the immobilization of 4-[4-(6-phosphonic acid-hexanoxyl)phenylazo]benzenesulfonic acid onto zirconium phosphonate. This catalyst was characterized by Fourier transform infrared, scanning electron microscopy, X-ray powder diffraction, nitrogen adsorption-desorption and UV–vis analyses. The catalytic activity of ZrOPPAZOSO3H was investigated towards the one-pot three-component Mannich-type reaction of benzaldehyde, aniline and cyclohexanone in water at room temperature, and gave excellent yields. Interestingly, the catalytic activity could be regulated by photoirradiation. Furthermore, upon completion of the reaction, the product could be readily separated by extraction, and the water phase reused in the next run. Lastly, the catalyst could be readily recovered by centrifugation and reused up to six times without any discernible impact on its activity.

•Novel surface molecularly imprinted polymer on ZnO nanorods was synthesized.•ZnO-SMIP showed good selectivity toward uric acid in physiological fluids.•ZnO-SMIP displayed good photoresponsive properties.A photoresponsive surface molecularly imprinted polymer for uric acid in physiological fluids was fabricated through a facile and effective method using bio-safe and biocompatible ZnO nanorods as a support. The strategy was carried out by introducing double bonds on the surface of the ZnO nanorods with 3-methacryloxypropyltrimethoxysilane. The surface molecularly imprinted polymer on ZnO nanorods was then prepared by surface polymerization using uric acid as template, water-soluble 5-[(4-(methacryloyloxy)phenyl)diazenyl]isophthalic acid as functional monomer, and triethanolamine trimethacryl ester as cross-linker. The surface molecularly imprinted polymer on ZnO nanorods showed good photoresponsive properties, high recognition ability, and fast binding kinetics toward uric acid, with a dissociation constant of 3.22 × 10− 5 M in aqueous NaH2PO4 buffer at pH = 7.0 and a maximal adsorption capacity of 1.45 μmol g− 1. Upon alternate irradiation at 365 and 440 nm, the surface molecularly imprinted polymer on ZnO nanorods can quantitatively uptake and release uric acid.

Detection of mercapto-containing pesticides plays a crucial role in food and water safety. A new Re(I)–NCS–Pt(II) complex, [Re(4,4′-di-tert-butyl-2,2′-bipyridine)(CO)3(NCS)]–[Pt(DMSO)(Cl)2] (1), was synthesized and characterized. The synthetic procedure, characterization results, and photophysical data for 1 are reported in this paper. Solvated complex 1 demonstrated luminescent chemodosimetric selectivity for phorate, demeton, and aldicarb (three common mercapto-containing pesticides) with method detection limits (MDLs) of 1.00, 2.87, and 2.08 ppm, respectively. The binding constants (log K) of 1 toward them were in the 3.24–3.44 range. The analyte selectivity of the complex was found to be dependent on the bridging linkage (C≡N and N═C═S) between the Re(I) and Pt(II) centers. The solid-supported dosimetric device 1 was fabricated by blending complex 1 with Al2O3 and poly(vinyl chloride) (PVC) powder. The MDLs of the device toward the mercapto-containing pesticides were 0.48–0.60 ppm. The device was applicable to pesticides in real water bodies such as taps, rivers, lakes, and underground water bodies with excellent recoveries and relative standard deviations of 76.2–108.0% and 2.9–6.7%, respectively. Its spectrofluorimetric changes could be analyzed by naked eye within 20 min with a linear luminometric response toward increases in the phorate concentration (0–8.0 ppm) with R = 0.999.

•Protonated Brooker's Merocyanine functionalised polymer microspheres was designed.•The microspheres display colorimetric and fluorescent sensing properties toward CN–.•The microspheres can be reversed for many times for monitoring and detection of CN–.•The microspheres are applicable for determination of CN– in real samples.This paper describes the development of a colorimetric and fluorescent cyanide probe based on crosslinked polymer microspheres functionalized with a protonated merocyanine. The functionalised microspheres were prepared by free radical polymerization using 4-((E)-2-[(4-hydroxylphenyl) ethenyl-1-allyl pyridinium bromide as the functional monomer, ethylene glycol dimethacrylate as the crosslinker, and azobisisobutylnitrile as the radical initiator. Upon introducing CN– to a suspension of the functionalised microspheres in ethanol/H2O (9:1, v/v), a change from yellow to red and a decrease in fluorescence intensity at 497 nm were immediately observed. This CN– probe can be reversed many times, which is cost efficient and beneficial to the environment. Analytical application of the functionlised microspheres to measure CN– concentration in spiked water samples was explored with good recoveries. Thus, the colorimetric and fluorescent CN− probe has high potential for the ultrasensitive detection of CN− in real samples.

•A novel photoresponsive molecularly imprinted polymer (MIP) for selective recognition of guanine in aqueous media is developed.•The MIP displays good selectivity toward guanine over other competing compounds.•The MIP can efficiently extract guanine from complicated beer and then photocontrolled release it in aqueous media for quantitative analysis.A novel photoresponsive molecularly imprinted polymer (MIP) was developed for the selective extraction of guanine from complex samples. The photoresponsive MIP was fabricated using guanine as the template, water-soluble 5-[(4-(methacryloyloxy)phenyl)diazenyl]isophthalic acid as the functional monomer, and water-soluble triethanolamine trimethacrylate as the cross-linker. The MIP displayed good selectivity toward guanine with a dissociation constant of (2.70 ± 0.16) × 10−5 mol L−1 in aqueous media. The density of the guanine-specific receptor sites in the MIP material was (4.49 ± 0.22) μmol g−1. Quantitatively release and uptake of guanine by the MIP occured with irradiation at 365 and 440 nm, respectively. The MIP could efficiently extract guanine from beer and then release it into aqueous media under photocontrol. This method could be used for selective separation and subsequent determination of a specific analytes from complex samples.

An L-proline-catalyzed aldol reaction was photo-controlled using an L-proline-imprinted polymer containing azobenzene. Upon UV irradiation, azobenzene chromophores underwent trans → cis isomerization, thereby releasing L-proline to catalyze the aldol reaction.

This study aimed to develop a recyclable, fluorescent, and colorimetric sensor for fluoride anion (F−) in aqueous media with fast response, good selectivity, and high sensitivity. A crosslinked polymer CpA1T5 was designed and synthesized as a sensor using (E)-1-allyl-4-((4-hydroxylphenyl)vinyl) quinolinium bromide as functional monomer, trimethylolpropane trimethacrylate as crosslinker, and azobisisobutyronitrile as initiator. When F− was introduced to the CpA1T5 suspension in deionized water, a change in color from gray to yellow and fluorescence enhancement accompanied with a redshift from 531 nm to 540 nm of fluorescence emission were immediately observed. This F− sensor can be recycled many times, making it cost efficient and beneficial to the environment. Analytical application of CpA1T5 to measure F− concentration in two commercial mouthwash samples was explored with good accuracy.

A colorimetric cyanide ion (CN−) sensor 4-[(1E)-2-(2-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (2-HPEAPB) was synthesized via condensation and N-alkylation reactions using 4-methylpyridine and salicylaldehyde as the starting materials. 2-HPEAPB displayed good selectivity, fast response, and high sensitivity toward CN− over other competing anions in acetonitrile–water (95:5, v/v) with a limit of detection of 8.0 × 10−6 mol L−1 by the naked eye. The sensing mechanism and the influence of pH and temperature on sensing properties were investigated. Colorimetric test paper for CN− was prepared by absorption of 2-HPEAPB to a chromatography paper, which could be used to detect CN− directly and quickly. Analytical application of measuring CN− concentration in an electroplating wastewater in real-time was conducted successfully.

Novel electrochromic and photoresponsive materials based on azobenzene-4,4′-dicarboxylic acid dialkyl ester derivatives (ADDEDs) were successfully prepared and characterized through nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and high-performance liquid chromatography-mass spectrometry. The electrochromic behavior, electrochromic mechanism, electro-optical properties, and photoresponsive properties of ADDEDs were investigated through cyclic voltammetry and ultraviolet-visible absorption spectra. ADDEDs displayed not only outstanding electrochromic behavior but also good and reversible photoisomerization properties even under electrochromic conditions. Electrochromic devices (ECDs) based on ADDEDs were fabricated, and their electrochromic performance was analyzed. The ECDs presented a color change from colorless to magenta between 0.0 V (bleached state) and ±3.0 V (colored state). In addition, the ECDs exhibited fast switching times, reasonable contrast, satisfactory optical memories, and redox stability. The novel redox-active azobenzene derivatives are promising candidates for full-color EC display devices, electronic paper, smart windows, optical memory devices, dual-stimuli-responsive systems, as well as other potential new applications.

•A colorimetric chemodosimeter (AHPEQB) based on quinolinium for cyanide ion was designed.•AHPEQB displays rapid response, good sensitivity, reversibility and selectivity toward cyanide ion among other competing anions in ethanol.•AHPEQB can be used for the ultrasensitive determination of cyanide ion concentration in real samples.A novel colorimetric chemodosimeter for cyanide (CN−) and 1-allyl-4-[2-(4-hydroxyphenyl)ethenyl)]-quinolinium bromide (AHPEQB) was designed and synthesized by condensation and terminal N alkyl reaction. AHPEQB exhibited highly selective and sensitive recognition properties toward CN− over other competing anions in ethanol, a protic solvent, with a 1:1 binding stoichiometry and a detection limit of 1.7 × 10−6 mol L−1. AHPEQB also displayed rapid colorimetric response that could be readily observed by the naked eye and good reversibility. The sensing mechanism of the proposed chemodosimeter was studied by UV–Vis, 1H NMR titration, and comparison 1-allyl-4-[2-(4-acetoxyphenyl)ethenyl)]-quinolinium bromide (AAPEQB). The colorimetric chemodosimeter showed high accuracy in determining the concentration of CN− in real water samples.

Photoresponsive surface molecular imprinting polymer (SMIP) microspheres were synthesized on silica microspheres by surface polymerization using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid as the functional monomer. The SMIP microspheres displayed good photoresponsive properties and specific affinity towards bisphenol A (BPA) with high recognition ability (maximal adsorption capacity: 6.96 μmol g−1) and fast binding kinetics (binding constant: 2.47 × 104 M−1) in aqueous media. Upon alternate irradiation at 365 and 440 nm, the SMIP microspheres could quantitatively bind and release BPA. Analytical application of the SMIP microspheres for the detection of trace BPA concentration in mineral water and tap water has been carried out successfully, and therefore a simple and quick detection method for trace BPA in the environment was established.

This Letter aimed to develop an efficient method for the determination of cyanide ion (CN−). A novel colorimetric chemosensor 4-[(1E)-2-(4-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (HPEAPB) was synthesized. HPEAPB displayed good selectivity toward CN− over other competing anions in ethanol. A color change from yellow to red was immediately observed upon the addition of CN− and the limit of detection (LOD) was 3.4 × 10−6 mol L−1. The sensing mechanism was discussed by UV–vis, 1H NMR titration, and a comparison study. Colorimetric test paper for CN− was prepared by attaching HPEAPB to a chromatography paper, which could be used to detect CN− in environmental samples as simply as a pH-indicator paper for pH value. The LOD of the test paper for CN− was 2.0 × 10−4 mol L−1. This detection method for CN− has potential applications in cyanide ion containing fields by combination of rapid and real-time advantages.

A novel turn-on fluorescent synthetic molecular probe for Hg2+ sensing in water based on 8-hydroxyquinoline is presented.

In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 × 104 M−1 in aqueous Tris–HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 μmol g−1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.

A photo-responsive molecularly imprinted sol–gel organic-inorganic hybrid material prepared by covalent imprinting of the template-functional monomer complex formed between 4,4′-dihydroxylazobenzene and ibuprofen was developed to explore the photo-regulated uptake and release of drug by a silicate-based smart molecularly imprinted materials. After imprinting, the template molecules (ibuprofen) were removed via hydrolysis in acid, and accurate cavities were left, which could be used as the receptor recognition sites for ibuprofen. The new organic–inorganic hybrid material shows specific affinity to ibuprofen and reversible uptake and release of ibuprofen upon alternate irradiation at 365 and 440 nm, respectively. The favorable binding strength of the imprinted receptor sites in the molecularly imprinted polymer (MIP) for ibuprofen is found to be 2.28 × 103 M−1. Density of receptor sites in the MIP material was 4.0 µmol/g—MIP.

The primary objective of this work is to explore the photoresponsive molecular recognition directed by fluorine–fluorine interaction. A new kind of fluorine-substituted photoresponsive functional monomer, (4-methacryloyloxy) nonafluoroazobenzene (MANFAB), was designed and synthesized, and a photoresponsive molecularly imprinted polymer containing a fluorine-substituted azobenzene chromophore (MIPF) was then fabricated using MANFAB as the monomer and 2,3,4,5,7,8,9,10-octafluorophenazine (PAF) as the model template. The photoisomerization process of MIPF materials is reversible. The release and uptake of PAF from toluene is photoregulated by alternate irradiation at 315 nm and 440 nm, indicating that photoresponsive molecular recognition directed by fluorine–fluorine interaction is possible. The binding strength of the imprinted receptor sites in MIPF for PAF is 4.67 × 104 M−1. The density of receptor sites in the MIPF material is 1.26 μmol/g-MIPF.

A novel dual responsive nanomaterial sensitive to both photo- and pH stimuli has been successfully developed. The polymer-based nanoparticles were fabricated from a specially designed photo- and pH-responsive amino-substituted azobenzene monomer, 4-amino-4′-methacrylatylazobenzene (AMAAB), via free radical polymerization with trimethylolpropane trimethacrylate (TRIM) cross-linkers. The trans-cis photoisomerization properties of AMAAB were retained after incorporation into the rigid three-dimensional cross-linked polymer matrix. The TRIM/AMAAB molar ratio significantly influenced the kinetics of the trans-cis photoisomerization. The nanoparticles also possessed good pH-responsive properties. The change in absorbance with media pH was monitored at 402 nm, and a “titration type” curve was obtained with a pKa value of 0.61 ± 0.06. At this transition point, the color of the nanoparticle suspension changed colour from yellow to pink. Thermogravimetric analysis (TGA) indicated that the nanoparticles were thermally stable.

A novel turn-on fluorescent synthetic molecular probe for Hg2+ sensing in water based on 8-hydroxyquinoline is presented.

A novel dual responsive nanomaterial sensitive to both photo- and pH stimuli has been successfully developed. The polymer-based nanoparticles were fabricated from a specially designed photo- and pH-responsive amino-substituted azobenzene monomer, 4-amino-4′-methacrylatylazobenzene (AMAAB), via free radical polymerization with trimethylolpropane trimethacrylate (TRIM) cross-linkers. The trans-cis photoisomerization properties of AMAAB were retained after incorporation into the rigid three-dimensional cross-linked polymer matrix. The TRIM/AMAAB molar ratio significantly influenced the kinetics of the trans-cis photoisomerization. The nanoparticles also possessed good pH-responsive properties. The change in absorbance with media pH was monitored at 402 nm, and a “titration type” curve was obtained with a pKa value of 0.61 ± 0.06. At this transition point, the color of the nanoparticle suspension changed colour from yellow to pink. Thermogravimetric analysis (TGA) indicated that the nanoparticles were thermally stable.

In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 × 104 M−1 in aqueous Tris–HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 μmol g−1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.

Novel electrochromic and photoresponsive materials based on azobenzene-4,4′-dicarboxylic acid dialkyl ester derivatives (ADDEDs) were successfully prepared and characterized through nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and high-performance liquid chromatography-mass spectrometry. The electrochromic behavior, electrochromic mechanism, electro-optical properties, and photoresponsive properties of ADDEDs were investigated through cyclic voltammetry and ultraviolet-visible absorption spectra. ADDEDs displayed not only outstanding electrochromic behavior but also good and reversible photoisomerization properties even under electrochromic conditions. Electrochromic devices (ECDs) based on ADDEDs were fabricated, and their electrochromic performance was analyzed. The ECDs presented a color change from colorless to magenta between 0.0 V (bleached state) and ±3.0 V (colored state). In addition, the ECDs exhibited fast switching times, reasonable contrast, satisfactory optical memories, and redox stability. The novel redox-active azobenzene derivatives are promising candidates for full-color EC display devices, electronic paper, smart windows, optical memory devices, dual-stimuli-responsive systems, as well as other potential new applications.

A colorimetric cyanide ion (CN−) sensor 4-[(1E)-2-(2-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (2-HPEAPB) was synthesized via condensation and N-alkylation reactions using 4-methylpyridine and salicylaldehyde as the starting materials. 2-HPEAPB displayed good selectivity, fast response, and high sensitivity toward CN− over other competing anions in acetonitrile–water (95 : 5, v/v) with a limit of detection of 8.0 × 10−6 mol L−1 by the naked eye. The sensing mechanism and the influence of pH and temperature on sensing properties were investigated. Colorimetric test paper for CN− was prepared by absorption of 2-HPEAPB to a chromatography paper, which could be used to detect CN− directly and quickly. Analytical application of measuring CN− concentration in an electroplating wastewater in real-time was conducted successfully.