Extraction of azo dyes by polyurethane foam

The extraction of 12 closely related mono-azo dyes by polyester and polyether-type polyurethane foams was studied to gain more information regarding the mechanism of the extraction of organic compounds. The effects on extraction of solution pH, dye concentration and salt concentration were investigated. It was found that the extraction of the dyes involved a neutral zwitterionic species and is highly dependent on the parameters studied. The dependency of the extraction on these parameters can be explained in a manner consistent with solvent extraction; however, the dual-mode sorption mechanism seems a more likely model. This mechanism involves both absorption related to solvent extraction, and an added component for surface adsorption. While the dual-mode sorption model explains the observed extraction behaviour, the data suggest that surface adsorption plays a much larger role than previously considered.     

Potentiometric study of silver(I)-thiosemicarbazonates

A potentiometric method is described for the determination of thiosemicarbazones involving the formation of a complex with Ag(I). This method is proposed for thiosemicarbazones of the following carbonyl compounds: salicylaldehyde, p-hydroxybenzaldehyde, benzaldehyde, picolinaldehyde, 6-methylpicolinaldehyde and p-dimethylaminebenzaldehyde. Stability constants of the complexes are determined by Ringbom and Harju's method.

FIG. 2. Variation of pAg + logα_{PAT (H)} + log ([Ag?PAT)]/[PAT])

2. Formation Constants of the Silver-Thiosemicarbazonates

     

4.

Phycocyanin-sensitized photoreduction of azo dyes     

J S Bellin  C A Gergel 《Photochemistry and photobiology》1969,10(6):427-439

Abstract— Phycocyanin can sensitize the photobleaching of azo dyes in a reaction which is analogous to one sensitized by chlorophyll. The quantum yield of the phycocyanin-sensitized photobleaching of congo red is low compared to the analogous reaction as sensitized by chlorophyll in aqueous pyridine. A kinetic mechanism for the former reaction is proposed and it was found that the manner in which phycocyanin sensitizes photoreduction of azo dyes is in several respects similar to that proposed for chlorophyll.     

5.

A spectral study of some azo dyes of biological importance     

《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1980,36(3):279-284

The u.v.-visible spectrophotometric behaviour of four textile dyes containing between one and four azo linkages has been studied over the pH range 1–13 and the pK_a values determined. Those dyes containing a hydroxy group adjacent to the azo linkage exhibited high pK_a values (⪢11) consistent with hydrogen bonding between the hydroxy and azo groups. These pK_a values have been assigned to their protonation—deprotonation sites within the molecules by consideration of the magnitude of the pK_a values and the direction of shift of the absorption maxima on passing through these values. It is recommended that the dyes are best identified in aqueous solution, pH = 8, and that ion exchange chromatography would be a necessary prerequisite for their determination in effluent discharge.     

6.

Dual-mode sorption of nonionic azo dyes by Nylon 6     

Takao Shibusawa  Yasuhiro Chigira 《Journal of Polymer Science.Polymer Physics》1992,30(6):563-568

Sorption isotherms of 2,4-dinitroaniline and three 4-amino-azobenzene derivatives (nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual-mode sorption model, Nernst-type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystalline phase.     

7.

Analyses of two azo dyes by high-performance liquid chromatography     

A Shan  D Harbin  C W Jameson 《Journal of chromatographic science》1988,26(9):439-442

Two structurally similar azo dyes, Direct Blue No. 6 and Direct Blue No. 15, are analyzed by separate reversed-phase high-performance liquid chromatographic (HPLC) systems utilizing a dual-wavelength UV/visible detector at 254 and 546 nm. Each dye contains more than 35 impurity peaks. Different lots of each dye are compared by means of their respective chromatographic profiles. The system used to obtain a chromatographic profile for each dye is adapted to make comparisons of the major component in different lots by an internal standard method. These methods are reproducible, giving relative standard deviations ranging from approximately 1 to 5%. These HPLC systems are adaptable for the analysis of other structurally similar dyes.     

8.

Organoiron polymers containing azo dyes     

Alaa S. Abd-El-Aziz  Erin K. Todd  Rawda M. Okasha  Tarek H. Afifi 《Macromolecular Symposia》2003,196(1):89-99

The synthesis of cationic organoiron polymers with azobenzene moieties in their side chains has been accomplished via nucleophilic aromatic substitution and ring-opening metathesis polymerization (ROMP) reactions. Polyaromatic ethers and thioethers with azobenzene moieties in their side chains were functionalized with different chromophores to yield yellow-, orange- and red-colored polymers. Polynorbornenes with azobenzene-containing side chains were isolated following ROMP of their monomeric analogs. All of the organoiron polymers were soluble in polar organic solvents and underwent reversible electrochemical reduction processes. Photobleaching of the azobenzene-containing polymers was achieved in the presence of hydrogen peroxide. The metallated polymers had glass transition temperatures approximately 50 to 80°C higher than their organic analogs.     

9.

Potentiometric study of silver complexes with thiourea in acid media     

《Journal of Coordination Chemistry》2012,65(16):2528-2535

Formation of silver complexes with thiourea in three different acids (perchloric, methanesulfonic, and sulfamic) was studied potentiometrically using modified Leden's method. It was established that, under conditions similar to the ones used for commercial electroplating of silver alloys, silver and thiourea form predominantly binuclear complexes Ag₂tu _n (n =?1–6). Calculated complex stability constants were similar in all cases suggesting that the acidity and the type of anion have little effect on the structure.     

10.

A physiochemical study of azo dyes: DFT based ESIPT process     

Jayabharathi J  Thanikachalam V  Perumal MV  Srinivasan N 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,83(1):200-206

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.     

11.

Influence of experimental conditions on the liquid secondary ion mass spectra of sulfonated azo dyes     

Susan D. Richardson  Alfred D. Thruston  John M. McGuire  George L. Baughman 《Journal of mass spectrometry : JMS》1991,26(10):826-830

Two monosulfonated and eight disulfonated azo dyes of varying relative molecular mass were examined by liquid secondary ion mass spectrometry (LSIMS). The effects of matrix, concentration, primary beam energy, and mode of operation were addressed in order to optimize sample ionization, whilst minimizing interference from matrix ions. Seven matrices were investigated: glycerol, thioglycerol, 3-nitrobenzyl alcohol, diethanolamine, 2-hydroxyethyl disulfide, a 1:1 (v/v) mixture of 2-hydroxyethyl disulfide and thioglycerol, and a 1 : 3 (v/v) mixture of dithioerythritol and dithiothreitol. Of these matrices, 3-nitrobenzyl alcohol produced LSIMS spectra that exhibited the most intense sample ions and the least inteiference from matrix ions. Minimum concentrations of 0.4 μg/μl and 4 μg/μl (dye in matrix) were necessary to produce useful full-scan spectra for monosulfonated azo dyes and disulfonated azo dyes, respectively; maximum sample ion intensities were obtained with concentrations ranging from 20 μg/μl to 60 μg/μl. A primary ion beam (cesium) of 10 to 15 kV produced the greatest secondary ionization efficiency, and a negative-ion analysis mode produced more useful spectra than those obtained in the positive-ion mode.     

12.

Oxidation of azo dyes in aqueous solutions by combined methods     

A. A. Batoeva  M. R. Sizykh 《Russian Journal of Applied Chemistry》2012,85(1):76-80

Fundamental aspects of the oxidative destruction of Orange III azo dye in aqueous solutions by integrated methods combining UV irradiation and iron-peroxide treatment were studied.     

13.

Soluble polymer-supported catalysts containing azo dyes     

Bergbreiter DE  Osburn PL  Li C 《Organic letters》2002,4(5):737-740

[structure: see text] Azo benzene derivatives were incorporated into soluble polymer-bound catalysts by two different approaches. The first was to attach the dye to the polymer-bound catalysts, using the dye as an innocent spectator to study the phase preference, concentration, and recoverability of a catalyst. The second approach used an azo dye as a ligand to form an effective soluble polymer-bound Pd(II) catalyst for Heck reactions.     

14.

Potentiometric determination of silver with dithiooxamide     

Lee H. Kalbus  Gene E. Kalbus 《Analytica chimica acta》1967

Potentiometric titration with dithiooxamide solution can be used to determine silver in the 0.0100–50.0 p.p.m range with an average accuracy of ca. 0.5% and a relative standard deviation ranging from 1.26% to 0.03% The metals commonly associated with silver can be masked with fluoride and EDTA The advantages of the method over other potentiometric and common spectrophotometric methods are outlined.     

15.

Structural characterization of sulfonated azo dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry     

Susan D. Richardson  John M. McGuire  Alfred D. Thruston  George L. Baughman 《Journal of mass spectrometry : JMS》1992,27(3):289-299

Eight monosulfonated and disulfonated azo dyes were analyzed using liquid secondary ion mass spectrometry/tandem mass spectrometry, in the negative ion mode, under low-energy collision conditions (110–150 eV). Many structurally characteristic fragment ions were obtained, several of which have not been reported previously using other mass spectrometric techniques. Among the structurally important ions observed were those due to loss of SO₂, SO₃ and various aromatic substituents, such as NO₂ and NHCOCH₃. Losses of N₂ were also proposed. In addition, product ions due to cleavage at the azo linkage were observed, and also SO₃^? and HSO₃^? ions. Several of the azo cleavage product ions detected did not contain sulfonate groups. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to better characterize and identify sulfonated azo dyes in the future.     

16.

Aminophenyl-X-azolopyridines as precursors of heterocyclic azo dyes     

P. Savarino  G. Viscardi  R. Carpignano  A. Borda  E. Barni 《Journal of heterocyclic chemistry》1989,26(2):289-292

Aminophenyl-X-azolopyridines (X = O, S, NH) are interesting intermediates for the synthesis of disperse azo dyes and, provided the pyridine nitrogen is quaternized, of their cationic counterparts. A set of novel amines and nitro derivatives is described, and their physical properties and spectral parameters are discussed in comparison with those of analogous compounds. Some dyes in the oxazole series function as probes of the reactivity of the pentatomic ring.     

17.

Decolorization and partial degradation of selected azo dyes by methanogenic sludge     

Yemashova N  Telegina A  Kotova I  Netrusov A  Kalyuzhnyi S 《Applied biochemistry and biotechnology》2004,119(1):31-40

The toxicity potential and decolorization of three acid azo dyes (Acid Orange 6, Acid Orange 7, and Acid Orange 52) by methanogenic granular sludge from an anaerobic expanded granular sludge bed reactor was assayed. Complete bioreduction was found for all three azo dyes. Sulfanilic acid and 4-aminoresorcinol were detected from the decolorization of Acid Orange 6, sulfanilic acid and 1-amino-2-naphtol were detected from the reduction of Acid Orange 7, and sulfanilic acid and N,N-dimethyl-1,4-phenylenediamine (DMP) were found to be intermediates of Acid Orange 52 degradation. Sulfanilic acid and 1-amino-2-naphtol were persistent in the anaerobic conditions, whereas 4-aminoresorcinol was completely mineralized by anaerobic sludge and DMP was transformed into 1,4-phenylenediamine. Enrichment cultures obtained via consecutive passages on basal medium with only azo dye as a carbon and an energy source seemed to be morphologically heterogeneous. Baculiform and coccus cells were found when viewed under a light microscope. Cocci were joined in chains. Because anaerobic sludge contains sulfate-reducing bacteria and therefore may generate sulfide, azo dyes were tested for chemical decolorization by sulfide to compare rates of chemical and biologic reduction.     

18.

Poly(organophosphazenes) containing azo dyes     

Giacomo Facchin  Mario Gleria  Francesco Minto  Roberta Bertani  Massimo Guglielmi  Giovanna Brusatin 《Macromolecular rapid communications》1995,16(3):211-217

In this paper we describe a method for the functionalization of catenapoly[bis(4-hydroxyphenoxy)-λ⁵-phosphazene] with diazonium salts to form new, deeply-coloured, phosphazene copolymers containing variable amounts of azo dyes attached to the polyphosphazene skeleton. The degree of functionalization in these substrates is regulated in order not to exceed 20% of the sites available in the pristine polyphosphazene and to maintain a high percentage of unreacted, free, hydroxy groups, in the final, coloured copolymers. These species are still very reactive and able to undergo further functionalization reactions.     

19.

QSRR approach in examining selected azo dyes     

Gyöngyi Vastag  Suzana Apostolov  Borko Matijević  Fathi Assaleh 《液相色谱法及相关技术杂志》2016,39(14):674-681

     

20.

Visible and near-infrared light activated azo dyes     

《中国化学快报》2021,32(8):2359-2368

The photoisomerization properties of azo derivatives have been widely used in the fields of materials and biology.One serious restriction to the development of functional azo-based materials is the necessity to trigger switching by UV light,which damage the corresponding surfaces and penetrate only partially through the matter.Therefore,developing the visible and near-infrared light activated azo switches can solve this problem.This review provides a summary of molecular design strategies for driving the isomerization of azo derivatives with visible light and near-infrared light:(1) smart design directly excited by visible light,(2) the addition of upconversion nanoparticles,(3) the employment of twophoton absorption,(4) indirect excitation in combination with metal sensitizer.     

Thiosemicarbazone	Log $\text{K}{}_{\mathrm{<mtext>f</mtext>}}$
-Benzaldehyde	15.5 ± 0.1
-Picolinaldehyde	14.0 ± 0.
-6-Methylpicolinaldehyde	14.5 ± 0.
-Salicylaldehyde	15.7 ± 0.1
-p-Hydroxybenzaldehyde	15.6 ± 0.
-p-Dimethylaminebenzaldehyde	17.2 ± 0.1

Phycocyanin-sensitized photoreduction of azo dyes

Abstract— Phycocyanin can sensitize the photobleaching of azo dyes in a reaction which is analogous to one sensitized by chlorophyll. The quantum yield of the phycocyanin-sensitized photobleaching of congo red is low compared to the analogous reaction as sensitized by chlorophyll in aqueous pyridine. A kinetic mechanism for the former reaction is proposed and it was found that the manner in which phycocyanin sensitizes photoreduction of azo dyes is in several respects similar to that proposed for chlorophyll.     

A spectral study of some azo dyes of biological importance

The u.v.-visible spectrophotometric behaviour of four textile dyes containing between one and four azo linkages has been studied over the pH range 1–13 and the pK_a values determined. Those dyes containing a hydroxy group adjacent to the azo linkage exhibited high pK_a values (⪢11) consistent with hydrogen bonding between the hydroxy and azo groups. These pK_a values have been assigned to their protonation—deprotonation sites within the molecules by consideration of the magnitude of the pK_a values and the direction of shift of the absorption maxima on passing through these values. It is recommended that the dyes are best identified in aqueous solution, pH = 8, and that ion exchange chromatography would be a necessary prerequisite for their determination in effluent discharge.     

Dual-mode sorption of nonionic azo dyes by Nylon 6

Sorption isotherms of 2,4-dinitroaniline and three 4-amino-azobenzene derivatives (nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual-mode sorption model, Nernst-type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystalline phase.     

Analyses of two azo dyes by high-performance liquid chromatography

Two structurally similar azo dyes, Direct Blue No. 6 and Direct Blue No. 15, are analyzed by separate reversed-phase high-performance liquid chromatographic (HPLC) systems utilizing a dual-wavelength UV/visible detector at 254 and 546 nm. Each dye contains more than 35 impurity peaks. Different lots of each dye are compared by means of their respective chromatographic profiles. The system used to obtain a chromatographic profile for each dye is adapted to make comparisons of the major component in different lots by an internal standard method. These methods are reproducible, giving relative standard deviations ranging from approximately 1 to 5%. These HPLC systems are adaptable for the analysis of other structurally similar dyes.     

Organoiron polymers containing azo dyes

The synthesis of cationic organoiron polymers with azobenzene moieties in their side chains has been accomplished via nucleophilic aromatic substitution and ring-opening metathesis polymerization (ROMP) reactions. Polyaromatic ethers and thioethers with azobenzene moieties in their side chains were functionalized with different chromophores to yield yellow-, orange- and red-colored polymers. Polynorbornenes with azobenzene-containing side chains were isolated following ROMP of their monomeric analogs. All of the organoiron polymers were soluble in polar organic solvents and underwent reversible electrochemical reduction processes. Photobleaching of the azobenzene-containing polymers was achieved in the presence of hydrogen peroxide. The metallated polymers had glass transition temperatures approximately 50 to 80°C higher than their organic analogs.     

Potentiometric study of silver complexes with thiourea in acid media

Formation of silver complexes with thiourea in three different acids (perchloric, methanesulfonic, and sulfamic) was studied potentiometrically using modified Leden's method. It was established that, under conditions similar to the ones used for commercial electroplating of silver alloys, silver and thiourea form predominantly binuclear complexes Ag₂tu _n (n =?1–6). Calculated complex stability constants were similar in all cases suggesting that the acidity and the type of anion have little effect on the structure.     

A physiochemical study of azo dyes: DFT based ESIPT process

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.     

Influence of experimental conditions on the liquid secondary ion mass spectra of sulfonated azo dyes

Two monosulfonated and eight disulfonated azo dyes of varying relative molecular mass were examined by liquid secondary ion mass spectrometry (LSIMS). The effects of matrix, concentration, primary beam energy, and mode of operation were addressed in order to optimize sample ionization, whilst minimizing interference from matrix ions. Seven matrices were investigated: glycerol, thioglycerol, 3-nitrobenzyl alcohol, diethanolamine, 2-hydroxyethyl disulfide, a 1:1 (v/v) mixture of 2-hydroxyethyl disulfide and thioglycerol, and a 1 : 3 (v/v) mixture of dithioerythritol and dithiothreitol. Of these matrices, 3-nitrobenzyl alcohol produced LSIMS spectra that exhibited the most intense sample ions and the least inteiference from matrix ions. Minimum concentrations of 0.4 μg/μl and 4 μg/μl (dye in matrix) were necessary to produce useful full-scan spectra for monosulfonated azo dyes and disulfonated azo dyes, respectively; maximum sample ion intensities were obtained with concentrations ranging from 20 μg/μl to 60 μg/μl. A primary ion beam (cesium) of 10 to 15 kV produced the greatest secondary ionization efficiency, and a negative-ion analysis mode produced more useful spectra than those obtained in the positive-ion mode.     

Oxidation of azo dyes in aqueous solutions by combined methods

Fundamental aspects of the oxidative destruction of Orange III azo dye in aqueous solutions by integrated methods combining UV irradiation and iron-peroxide treatment were studied.     

Soluble polymer-supported catalysts containing azo dyes

[structure: see text] Azo benzene derivatives were incorporated into soluble polymer-bound catalysts by two different approaches. The first was to attach the dye to the polymer-bound catalysts, using the dye as an innocent spectator to study the phase preference, concentration, and recoverability of a catalyst. The second approach used an azo dye as a ligand to form an effective soluble polymer-bound Pd(II) catalyst for Heck reactions.     

Potentiometric determination of silver with dithiooxamide

Potentiometric titration with dithiooxamide solution can be used to determine silver in the 0.0100–50.0 p.p.m range with an average accuracy of ca. 0.5% and a relative standard deviation ranging from 1.26% to 0.03% The metals commonly associated with silver can be masked with fluoride and EDTA The advantages of the method over other potentiometric and common spectrophotometric methods are outlined.     

Structural characterization of sulfonated azo dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry

Eight monosulfonated and disulfonated azo dyes were analyzed using liquid secondary ion mass spectrometry/tandem mass spectrometry, in the negative ion mode, under low-energy collision conditions (110–150 eV). Many structurally characteristic fragment ions were obtained, several of which have not been reported previously using other mass spectrometric techniques. Among the structurally important ions observed were those due to loss of SO₂, SO₃ and various aromatic substituents, such as NO₂ and NHCOCH₃. Losses of N₂ were also proposed. In addition, product ions due to cleavage at the azo linkage were observed, and also SO₃^? and HSO₃^? ions. Several of the azo cleavage product ions detected did not contain sulfonate groups. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to better characterize and identify sulfonated azo dyes in the future.     

Aminophenyl-X-azolopyridines as precursors of heterocyclic azo dyes

Aminophenyl-X-azolopyridines (X = O, S, NH) are interesting intermediates for the synthesis of disperse azo dyes and, provided the pyridine nitrogen is quaternized, of their cationic counterparts. A set of novel amines and nitro derivatives is described, and their physical properties and spectral parameters are discussed in comparison with those of analogous compounds. Some dyes in the oxazole series function as probes of the reactivity of the pentatomic ring.     

Decolorization and partial degradation of selected azo dyes by methanogenic sludge

The toxicity potential and decolorization of three acid azo dyes (Acid Orange 6, Acid Orange 7, and Acid Orange 52) by methanogenic granular sludge from an anaerobic expanded granular sludge bed reactor was assayed. Complete bioreduction was found for all three azo dyes. Sulfanilic acid and 4-aminoresorcinol were detected from the decolorization of Acid Orange 6, sulfanilic acid and 1-amino-2-naphtol were detected from the reduction of Acid Orange 7, and sulfanilic acid and N,N-dimethyl-1,4-phenylenediamine (DMP) were found to be intermediates of Acid Orange 52 degradation. Sulfanilic acid and 1-amino-2-naphtol were persistent in the anaerobic conditions, whereas 4-aminoresorcinol was completely mineralized by anaerobic sludge and DMP was transformed into 1,4-phenylenediamine. Enrichment cultures obtained via consecutive passages on basal medium with only azo dye as a carbon and an energy source seemed to be morphologically heterogeneous. Baculiform and coccus cells were found when viewed under a light microscope. Cocci were joined in chains. Because anaerobic sludge contains sulfate-reducing bacteria and therefore may generate sulfide, azo dyes were tested for chemical decolorization by sulfide to compare rates of chemical and biologic reduction.     

Poly(organophosphazenes) containing azo dyes

In this paper we describe a method for the functionalization of catenapoly[bis(4-hydroxyphenoxy)-λ⁵-phosphazene] with diazonium salts to form new, deeply-coloured, phosphazene copolymers containing variable amounts of azo dyes attached to the polyphosphazene skeleton. The degree of functionalization in these substrates is regulated in order not to exceed 20% of the sites available in the pristine polyphosphazene and to maintain a high percentage of unreacted, free, hydroxy groups, in the final, coloured copolymers. These species are still very reactive and able to undergo further functionalization reactions.     

Visible and near-infrared light activated azo dyes

The photoisomerization properties of azo derivatives have been widely used in the fields of materials and biology.One serious restriction to the development of functional azo-based materials is the necessity to trigger switching by UV light,which damage the corresponding surfaces and penetrate only partially through the matter.Therefore,developing the visible and near-infrared light activated azo switches can solve this problem.This review provides a summary of molecular design strategies for driving the isomerization of azo derivatives with visible light and near-infrared light:(1) smart design directly excited by visible light,(2) the addition of upconversion nanoparticles,(3) the employment of twophoton absorption,(4) indirect excitation in combination with metal sensitizer.