Kinetic Study of Thermal Z to E Isomerization Reactions of Azobenzene and 4‐Dimethylamino‐4′‐nitroazobenzene in Ionic Liquids [1‐R‐3‐Methylimidazolium Bis(trifluoromethylsulfonyl)imide with R=Butyl, Pentyl, and Hexyl]

Abstract

Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4'-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl, and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the viscosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4'-nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 10(4)-10(7) s(-1).

cis-to-trans isomerization of azobenzene investigated by using thin films of metal–organic frameworks

“…polymers, 4 liquid crystals, 3 or metal-organic frameworks. 17,18 To the best of our knowledge, all measurements reported previously were affected by such environmental effects. The trans-to-cis switching is driven by absorption of light.…”

“…25 Furthermore, SURMOFs can be studied in a straightforward fashion by surface-sensitive spectroscopic techniques like X-ray photoelectron spectroscopy (XPS) 26 and infrared reflection-absorption spectroscopy (IRRAS). Although this method has substantial advantages over UV-Vis spectroscopy, which is used in most other works to monitor the back-switching, 11,12,17,18 it is seldom employed, since the vibrational modes sensitive to the conformational change often have low excitation probabilities and since the background of the solvent or matrix often obscures the cisto-trans induced changes in the IR-spectra of the photoswitchable molecule. 27,28 Two pillared-layer MOF structures based on organic linker molecules with azobenzene side groups are investigated: Cu 2 (BDC) 2 (AzoBiPyB) and Cu 2 (DMTPDC) 2 (AzoBiPyB) (AzoBiPyB: 4,4 0 -(2-(phenyldiazenyl)-1,4-phenylene)dipyridine); 29 BDC: benzene-1,4-dicarboxylic acid, DMTPDC: 2,2 00 -dimethyl-[1,1 0 :4 0 ,1 00 -terphenyl]-4,4 00 -dicarboxylic acid, see ESI † (SI1).…”

Chemo-enzymatic Baeyer–Villiger oxidation in the presence of Candida antarctica lipase B and ionic liquids

“…Novozyme-35 was donated by Novozymes. Quarterisation 40 reactions of 1-methylimidazole or 1,2-dimethylimidzole, 24 3picoline, 25 and aliphatic amines, 26 metathesis reaction, 27 and synthesis of 3-substituted cyclobutanones 14 were performed according to literature methods. 45 1 H NMR and 13 C NMR spectra of the lactones were recorded at 300 MHz in CDCl3 (Varian Unity Inova plus spectrometer with a TMS internal standard).…”

Photoisomerization dynamics study on cis-azobenzene derivative using ultraviolet-to-visible tunable femtosecond pulses

“…In addition, the femtosecond photoisomerization of cis-azobenzene without substitution has been examined [4]. Moreover, the ground-state kinetics on thermal isomerization of azobenzene and 4-dimethylamino-4 0 -nitroazobenzene has been studied [5]. In those investigations the main focus has been on the inversion processes and the rotation processes in the photoisomerization mechanisms, but the assignment and time-dependent behaviors of the signal due to the isomer to be yielded in the ultrafast dynamics on the basis of the quantitative analysis have not been discussed clearly.…”