Dear Chandra,

You can find the rate constant of the cis-trans isomerization of azobenzene in different solvents in the following publications:

1-Rate constants of the thermal cis-trans isomerization of azobenzene dyes in solvents, acetone/water mixtures, and in microheterogeneous surfactant solutions

Authors

Kathrin Gille, Helmut Knoll, Konrad Quitzsch

First published: 16 April 1999Full publication history

DOI: 10.1002/(SICI)1097-4601(1999)31:53.0.CO;2-EView/save citation

Cited by: 16 articlesCitation tools

Abstract

Rate constants kiso of the thermal cis-trans isomerization of four 4,4’-nitro-aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to λmax from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on kiso- and λmax-values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted.

In microheterogeneous water/surfactant solutions kiso-values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton®X-100, C12EO8 in water, and varied with the composition of bicontinuous microemulsions of Igepal® CA-520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity.

Replacement of H2O by D2O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 337–350, 1999

http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-4601(1999)31:5%3C337::AID-KIN3%3E3.0.CO;2-E/full

2-Cis-Trans Isomerisation of Azobenzenes Studied by NMR Spectroscopy with In situ Laser Irradiation and DFT Calculations 

NUHA WAZZAN

https://core.ac.uk/download/files/39/279718.pdf

Hoping this will be helpful,

Rafik

Thank you Prof. Rafik. I have seen the links which you have posted. But in all the papers they calculated the rate constant for azobenzene in solvents. Is there any studies where anyone calculated the rate constant for the isomerization of azobenezene in gas phase (either theoretically or via experiment)

Dear Chandra,

Herein for the gas phase:

For azobenzene the thermal activation barrier lies at an energy of 96 kJ/mol [112]. Andersson and coworkers have shown in detail that this excitation mechanism is present for the cis-to-trans-isomerisation of azobenzenes[113, 114]. For photoinduced isomerisation, the excitation energies (wavelengths) are 3.55 eV (350 nm) for the trans-to-cis and 2.82 eV (440 nm) for the cis-to-trans-isomerisation[115, 116]. These are again direct n-π∗ excitations from an unbonding into an excited antibonding π∗ state of azobenzene comparable to the S1 state shown for stilbene in figure 5.5. While for stilbene only photoisomerisation has been investigated, for azobenzenes additional excitation mechanisms have been sought for. Besenbacher and coworkers showed for azobenzene on Cu(110) that the substrate - adsorbate interactions are as strong that additional thermal activation might be needed in conjunction with the photoexcitation[117].In this case, the azobenzenes adsorbed at the Cu bridge sites and with a small tilt angle along the direction. Morgenstern and coworkers showed that direct excitation of single azobenzene molecules by inelastic electron tunneling can induce the cis-to-trans and trans-to-cis isomerisation[116]. Excitation energies of about 640 meV and 650 meV had to be applied, respectively. Grill and coworkers showed, that also the electric field between STM-tip and metal (Au(111)) surface can induce isomerisation of azobenzene molecules[118].

For more, see the following link:

http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000003498/06_05_Isomerisation.pdf;jsessionid=123C28FE3DBED72A6F439FE3B78CE766?hosts=

Hoping this will be helpful,

Rafik