PRODUCTS

AZOBENZENE

Azobenzene is a versatile aromatic azo compound recognized for its reversible light-induced trans–cis isomerization.
Azobenzene is widely used in photoresponsive polymers, molecular switches, liquid crystals, optical devices, and advanced material research.
Azobenzene's controllable structural transformation under light makes azobenzene especially valuable in smart materials, sensors, nanotechnology, and photochemical applications.

CAS Number: 103-33-3
EC Number: 203-102-5
Molecular Formula: C12H10N2
Molecular Weight: 182.22 g/mol

Synonyms: Azobenzene, 1,2-Diphenyldiazene, 203-102-5, Azobenzeen, Azobenzide, Azobenzol, Azobisbenzene, Azodibenzene, Azodibenzeneazofume, Azofume, Benzene, azobis-, Benzene, azodi, Benzeneazobenzene, Benzofume, CHEBI:190358, DTXCID40123, DTXSID8020123, Diazene, 1,2-diphenyl-, Diazene, diphenyl-, Diazobenzene, Diphenyldiazene, Diphenyldiimide, ENT 14,611, F0U1H6UG5C, NCI-C02926, NSC-2102, RefChem:6878, USAF EK-704, 103-33-3, Azobenzene, Diazene, 1,2-diphenyl-, Diphenyldiazen, Diphenyldiazene, Diphényldiazène, 1,2-Diphenyldiazene, 103-33-3, 17082-12-1, 203-102-5, azobenzide, azobenzol, azobisbenzene, Azodibenzene, azodibenzeneazofume, azofume, BENZENEAZOBENZENE, benzofume, diazobenzene, Diphenyldiimide, MFCD00003022, PHENYLAZOBENZENE

Azobenzene is an aromatic azo compound consisting of two phenyl rings connected by an azo group (-N=N-).
Azobenzene is typically found as an orange-red to yellow crystalline solid and is well known for its reversible trans–cis photoisomerization when exposed to specific wavelengths of light.
Azobenzene is widely used in photoresponsive materials, molecular switches, liquid crystals, dyes, optical storage systems, and advanced polymer research.

Azobenzene is a photoswitchable chemical compound composed of two phenyl rings linked by a N=N double bond.
Azobenzene is the simplest example of an aryl azo compound.

The term "azobenzene" or simply "azo" is often used to refer to a wide class of similar compounds.
These azo compounds are considered as derivatives of diazene (diimide) and are sometimes referred to as "diazenes".

The diazenes absorb light strongly and are common dyes.
Different classes of azo dyes exist, most notably the ones substituted with heteroaryl rings.

Azobenzene can be used as an optical trigger for the design and synthesis of a large variety of photoresponsive systems.

Photochromic compounds that undergo large conformational changes when exposed to light of appropriate wavelength are particularly attractive as molecular switch elements.
Azobenzene is a popular choice among the chromophores.

The thermodynamically favored trans isomer is rapidly converted to the cis isomer by irradiation at the wavelength of the π-π* transition, whereas the reverse process is achieved either (slowly) by thermal relaxation in the dark or (quickly) by irradiation at the wavelength of the n-π* transition.
The azobenzene amino acid (aa) can be used as a photo-inducible conformational switch in polypeptides.

A reversible conformational change of the peptide backbone is induced by switching between the cis and trans configurations of the azobenzene moiety by irradiation with light of suitable wavelength.
Azobenzene has been the most widely used optical trigger for the synthesis of photoresponsive systems ranging from poly-a-amino acids to innovative materials with light-controlled mechanical and optical properties.

Azobenzene's use in form of appropriate derivatives allow to generate cyclic peptide structures of constraint conformational space and thus to exploit its reversible photoisomerization to induce well defined transitions between different conformational states.
Azobenzene photoswitches can be used to drive functional changes in peptides, proteins, nucleic acids, lipids, and carbohydrates.

Azobenzene is a phototrigger that can be used to design and synthesize a variety of photoresponsive systems.
Azobenzene is genotoxic and induces aggressive sarcomas of the spleen and other abdominal organs.

Azobenzene is used to construct photoswitch tethered ligands to turn protein activity on and off.
Azobenzene is also used to increase the extracellular or intracellular concentration of active molecules to study the mechanism of action of sympathetic and parasympathetic neuromediators.

Azobenzene is defined as a photochromic molecule whose structure and color change reversibly upon photo-irradiation, specifically through trans-to-cis isomerization with UV light and cis-to-trans isomerization with blue light.
Azobenzene appears as orange-red crystals or dark brown chunky solid.

Azobenzene is a chromogen and an azo compound that exhibits trans/cis isomerism yielding isomers that differ in color.
Azobenzene is a simple azoarene compound that shows cis-trans isomerization around the azo bond in response to light.

Azobenzene is a well-known derivative of stimulus-responsive molecular switches and has shown superior performance as a functional material in biomedical applications.
Azobenzene is a typical photo-responsive molecule that isomerizes from its planar trans-form to the non-planar cis-form after UV-light irradiation with a wavelength between 300 nm and 400 nm (lmax is around 330 nm).

Interestingly, the system reverts from the cis-form to the trans-form after further irradiation with visible light (wavelength over 400 nm).
This process is completely reversible, and the azobenzene group does not decompose or induce undesirable side reactions even on repeated trans-cis isomerization.

By introducing azobenzenes into DNA through D-threoninol as a linker, Asanuma and co-workers succeeded in achieving photo-regulation of:
Formation and dissociation of a DNA duplex
Transcription by T7-RNA polymerase reaction

Uses of Azobenzene:
Azobenzene is widely used in photoresponsive materials because it can reversibly switch between trans and cis forms under light exposure.
Azobenzene is applied in molecular switches, optical data storage, smart polymers, liquid crystal systems, and light-controlled actuators.
Azobenzene derivatives are also used in dyes, pigments, surface coatings, sensors, nanotechnology, and research on controlled drug-delivery systems.

Azobenzene is used as an acaricide, fumigant, and chemical intermediate (dyes, rubber accelerators, and polymers).
Azobenzene is formerly used as an intermediate for the production of benzidine, insecticides, and pyrazolone derivatives.

Azobenzene and its derivatives have multiple applications in the field of mechanical and optical materials, in photopharmacology, and molecular photo-switches including in biological probes.
As human tissue is translucent to red and near-infrared light but opaque to blue and UV light, Azobenzene is important in medicine and photopharmacology for applications that involve shifting the absorptions of both trans and cis isomers of azobenzene to longer wavelengths.

Production Methods of Azobenzene:
Azobenzene is commercially synthesised by the oxidative coupling of aniline using nitrosating agents or diazotisation followed by reduction.
The most common production route involves diazotizing aniline with sodium nitrite in acidic conditions to form benzenediazonium chloride, which is then reacted with another equivalent of aniline to yield azobenzene via electrophilic aromatic substitution.
Alternatively, oxidative coupling using agents like manganese dioxide or air oxidation can be employed.

Structure and Synthesis of Azobenzene:
Azobenzene was first described by Eilhard Mitscherlich in 1834.
Yellowish-red crystalline flakes of azobenzene were obtained in 1856.

Azobenzene's original preparation is similar to the modern one.
According to the 1856 method, nitrobenzene is reduced by iron filings in the presence of acetic acid.

In the modern synthesis, zinc is the reductant in the presence of a base.
Industrial electrosynthesis using nitrobenzene is also employed.

trans-Azobenzene isomer is planar with an N-N distance of 1.189 Å.
cis-Azobenzene is nonplanar with a C-N=N-C dihedral angle of 173.5° and an N-N distance of 1.251 Å.
The trans isomer is more stable by approximately 50 kJ/mol, and the barrier to isomerization in the ground state is approximately 100 kJ/mol.

Reactions of Azobenzene:
Azobenzene is a weak base, but undergoes protonation at one nitrogen with a pKa = -2.95.
Azobenzene functions as a Lewis base, e.g. toward boron trihalides.
Azobenzene binds to low valence metal centers, e.g. Ni(Ph2N2)(PPh3)2 is well characterized.

Azobenzene oxidizes to give azoxybenzene.
Hydrogenation gives diphenylhydrazine.

Trans–cis isomerization:
Azobenzene (and derivatives) undergo photoisomerization of trans and cis isomers.
cis-Azobenzene relaxes back, in dark, to the trans isomer.

Such thermal relaxation is slow at room temperature.
The two isomers can be switched with particular wavelengths of light: ultraviolet light, which corresponds to the energy gap of the π-π* (S2 state) transition, for trans-to-cis conversion, and blue light, which is equivalent to that of the n-π* (S1 state) transition, for cis-to-trans isomerization.

For a variety of reasons, the cis isomer is less stable than the trans (for instance, Azobenzene has a distorted configuration and is less delocalized than the trans configuration).
Photoisomerization allows for reversible energy storage (as photoswitches).

Spectroscopic classification:
The wavelengths at which azobenzene isomerization occurs depends on the particular structure of each azo molecule, but they are typically grouped into three classes: the azobenzene-type molecules, the aminoazobenzenes, and the pseudo-stilbenes.
These azos are yellow, orange, and red, respectively owing to the subtle differences in their electronic absorption spectra.

Azobenzenes similar to the unsubstituted azobenzene exhibit a low-intensity n-π* absorption in the visible region, and a much higher intensity π-π* absorption in the ultraviolet.
Azos that are ortho- or para-substituted with electron-donating groups (such as aminos), are classified as aminoazobenzenes, and tend to closely spaced n-π* and π-π* bands in the visible.

The pseudo-stilbene class is characterized by substituting the 4 and 4' positions of the two azo rings with electron-donating and electron-withdrawing groups (that is, the two opposite ends of the aromatic system are functionalized).
The addition of this push-pull configuration results in a strongly asymmetric electron distribution, which modifies a host of optical properties.

In particular, Azobenzene shifts the absorption spectra of the trans and the cis isomers, so that they effectively overlap.
Thus, for these compounds a single wavelength of light in the visible region will induce both the forward and reverse isomerization.
Under illumination, these molecules cycle between the two isomeric states.

Photophysics of isomerization:
The photo-isomerization of azobenzene is extremely rapid, occurring on picosecond timescales.
The rate of the thermal back-relaxation varies greatly depending on the compound: usually hours for azobenzene-type molecules, minutes for aminoazobenzenes, and seconds for the pseudo-stilbenes.[16]

The mechanism of isomerization has been the subject of some debate, with two pathways identified as viable: a rotation about the N-N bond, with disruption of the double bond, or via an inversion, with a semi-linear and hybridized transition state.
Azobenzene has been suggested that the trans-to-cis conversion occurs via rotation into the S2 state, whereas inversion gives rise to the cis-to-trans conversion.

Azobenzene is still under discussion which excited state plays a direct role in the series of the photoisomerization behavior.
However, the latest research utilizing femtosecond transient absorption spectroscopy has suggested that the S2 state undergoes internal conversion to the S1 state, and then the trans-to-cis isomerization proceeds.

Recently another isomerization pathway has been proposed by Diau the "concerted inversion" pathway in which both CNN bond angles bend at the same time.
There is experimental and computational evidence for the existence of a multistate rotation mechanism involving a triplet state.

Photoinduced motions:
The photo-isomerization of azobenzene is a form of light-induced molecular motion.
This isomerization can also lead to motion on larger length scales.

For instance, polarized light will cause the molecules to isomerize and relax in random positions.
However, those relaxed (trans) molecules that fall perpendicular to the incoming light polarization will no longer be able to absorb, and will remain fixed.

Thus, there is a statistical enrichment of chromophores perpendicular to polarized light (orientational hole burning).
Polarized irradiation will make an azo-material anisotropic and therefore optically birefringent and dichroic.
This photo-orientation can also be used to orient other materials (especially in liquid crystal systems).

Miscellaneous of Azobenzene:
Azobenzene undergoes ortho-metalation by metal complexes, e.g. dicobalt octacarbonyl.
Info about the carcinogenicity of Azobenzene can be found on the EPA site, where it has been classified as a "probable human carcinogen" based on evidence of carcinogenicity in animals.[24]

Stability and Reactivity of Azobenzene:

Chemical Stability:
Stable under normal ambient conditions and recommended storage conditions.

Reactivity:
No hazardous reactions are expected during normal handling and use.

Conditions to Avoid:
Excessive heat, ignition sources, dust formation, and prolonged exposure to incompatible materials.

Incompatible Materials:
Strong oxidizing agents and strong reducing agents.

Hazardous Decomposition Products:
Thermal decomposition or combustion may produce carbon monoxide, carbon dioxide, and nitrogen oxides.

Handling and Storage of Azobenzene:

Safe Handling:
Avoid breathing dust and prevent contact with skin and eyes.
Handle with adequate ventilation and use suitable personal protective equipment.

Storage Conditions:
Keep the container tightly closed in a cool, dry, and well-ventilated area.
Store away from incompatible materials and restrict access to trained or authorized personnel.

First Aid Measures of Azobenzene:

Inhalation:
Move the affected person to fresh air and obtain medical attention if exposure or symptoms occur.

Skin Contact:
Wash the affected area thoroughly with plenty of water and remove contaminated clothing.

Eye Contact:
Rinse cautiously with plenty of water for at least 15 minutes and seek medical attention.

Ingestion:
Rinse the mouth, do not induce vomiting, and contact a physician or poison control center.

Firefighting Measures of Azobenzene:

Suitable Extinguishing Media:
Use water spray, carbon dioxide, dry chemical powder, or chemical foam.

Specific Hazards:
Heating or combustion may generate irritating fumes and nitrogen oxides, carbon monoxide, and carbon dioxide.

Protective Equipment:
Firefighters should wear full protective clothing and a self-contained breathing apparatus.

Accidental Release Measures of Azobenzene:

Personal Precautions:
Ensure adequate ventilation, avoid dust formation, and wear appropriate personal protective equipment.

Environmental Precautions:
Prevent the material from entering drains, surface water, or the surrounding environment.

Cleanup Methods:
Carefully sweep or collect the spilled material without generating dust and place it in a suitable closed container for disposal.

Exposure Controls/Personal Protection of Azobenzene:

Engineering Controls:
Provide effective local exhaust ventilation, particularly where dust may be generated.

Eye Protection:
Wear chemical safety glasses or goggles.

Hand Protection:
Use suitable chemical-resistant protective gloves.

Skin Protection:
Wear appropriate protective clothing to minimize skin exposure.

Respiratory Protection:
Use suitable respiratory protection when adequate ventilation cannot be maintained or significant dust exposure may occur.

Identifiers of Azobenzene:
Linear Formula: C6H5N=NC6H5
CAS Number: 103-33-3
Molecular Weight: 182.22
UNSPSC Code: 12171500
NACRES: NA.47
PubChem Substance ID: 24866581
EC Number: 203-102-5
Beilstein/REAXYS Number: 1819138
MDL number: MFCD00003022

CAS No: 103-33-3
Chemical Name: Azobenzene
CBNumber: CB4383484
Molecular Formula: C12H10N2
Molecular Weight: 182.22
MDL Number: MFCD00003022
MOL File: 103-33-3.mol

CAS Number: 103-33-3
Beilstein Reference: 742610
ChEBI: CHEBI:58996
ChEMBL: ChEMBL58835
ChemSpider: 2185
ECHA InfoCard: 100.002.820
EC Number: 203-102-5
Gmelin Reference: 83610
KEGG: C19334
PubChem CID: 2272
RTECS number: CN1400000
UNII: F0U1H6UG5C
CompTox Dashboard (EPA): DTXSID8020123
InChI: InChI=1S/C12H10N2/c1-3-7-11(8-4-1)13-14-12-9-5-2-6-10-12/h1-10H/b14-13+
Key: DMLAVOWQYNRWNQ-BUHFOSPRSA-N
InChI=1/C12H10N2/c1-3-7-11(8-4-1)13-14-12-9-5-2-6-10-12/h1-10H/b14-13+
Key: DMLAVOWQYNRWNQ-BUHFOSPRBP
SMILES: N(=N/c1ccccc1)\c2ccccc2

Properties of Azobenzene:
Chemical formula: C12H10N2
Molar mass: 182.226 g·mol−1
Appearance: orange-red crystals
Density: 1.203 g/cm3
Melting point: 67.88 °C (trans), 71.6 °C (cis)
Boiling point: 300 °C (572 °F; 573 K)
Solubility in water: 6.4 mg/L (25 °C)
Acidity (pKa): −2.95 (conjugate acid)
Magnetic susceptibility (χ): −106.8·10−6 cm3/mol
Refractive index (nD): 1.6266 (589 nm, 78 °C)

Melting point: 65-68 °C (lit.)
Boiling point: 293 °C (lit.)
Density: 1.09 g/mL at 25 °C (lit.)
vapor pressure: 1 mm Hg ( 104 °C)
refractive index: 1.62662 (78.1℃)
Flash point: 100 °C
storage temp.: room temp
solubility: 6.4mg/l
form: Crystalline Powder
color: Orange
Water Solubility: Soluble in alcohol, ether, benzene and glacial acetic acid. Insoluble in water.
Merck: 14,917
BRN: 1819138
Henry's Law Constant: 7.3×10-1 mol/(m3Pa) at 25℃, Duchowicz et al. (2020)
Stability: Stable. Combustible. Incompatible with strong oxidizing agents. Air and light sensitive.
histology
InChI: 1S/C12H10N2/c1-3-7-11(8-4-1)13-14-12-9-5-2-6-10-12/h1-10H/b14-13+
InChIKey: DMLAVOWQYNRWNQ-BUHFOSPRSA-N
SMILES: c1ccc(cc1)\N=N\c2ccccc2
CAS DataBase Reference: 103-33-3(CAS DataBase Reference)
EWG's Food Scores: 4
FDA UNII: F0U1H6UG5C
Proposition 65 List: Azobenzene
IARC: 3 (Vol. 8, Sup 7) 1987
EPA Substance Registry System: Azobenzene (103-33-3)
UNSPSC Code: 12352124
NACRES: NA.47

vapor pressure: 1 mmHg ( 104 °C)
Quality Segment: 100
assay: 98%
form: powder or crystals
autoignition temp.: 890 °F
technique(s): titration: suitable
bp: 293 °C (lit.)
mp: 65-68 °C (lit.)
density: 1.09 g/mL at 25 °C (lit.)
storage temp.: room temp
SMILES string: c1ccc(cc1)\N=N\c2ccccc2
InChI: 1S/C12H10N2/c1-3-7-11(8-4-1)13-14-12-9-5-2-6-10-12/h1-10H/b14-13+
InChI key: DMLAVOWQYNRWNQ-BUHFOSPRSA-N

Specifications of Azobenzene:
Appearance (Color): Orange to red
Assay (GC): ≥97.0%
Identification (FTIR): Conforms
Form: Crystals or powder or crystalline powder or chunks
Melting Point (clear melt): 62.0-72.0?C

Structure of Azobenzene:
Molecular shape: sp2 at N
Dipole moment: 0 D (trans isomer)

Related Compounds of Azobenzene:
Nitrosobenzene aniline

Names of Azobenzene:

IUPAC name:
(E)-Diphenyldiazene

Other name:
Azobenzene