Effects of Solvent Fluctuations on the Rate of Thermal Z/E Isomerization of Azobenzenes and N-Benzylideneanilines

Abstract

Effects of pressure on thermal Z/E isomerization of substituted N-benzylideneanilines and azobenzenes were studied in 2-methyl-2,4-pentanediol. Pressure dependence of the Z/E isomerization of a substituted azonaphthalene was also studied in glycerol triacetate. From the results in this and earlier papers, the following conclusions were reached. 1) It is possible to cast slow thermal reactions into the state of fluctuation control in highly viscous liquid phase realized by a combination of a viscous liquid and high pressure. 2) The viscosity dependence of the rate constant can be rationalized by the two-dimensional reaction-coordinate model developed by Sumi but not by the Grote–Hynes’ theory of frequency-dependent friction. Namely, the energy-barrier crossing takes place after the solvent molecules are rearranged to accommodate the transition state. 3) Whether the solvent rearrangement involves chemical transformations with appreciable energy increases depends on the nature of the reaction and the solvent.

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]

“…In addition, the isomerization of DNAB had been found to enter the Kramers' “high viscosity region” only when the viscosity exceeded 10 4 cP (=10 Pa s) 37. 38 It also has to be pointed out that in this “diffusion‐controlled” region, the reaction was characterized by nonlinear Arrhenius plots with large downward deviations at low temperatures,37, 38 while the plots were linear in B‐IL, P‐IL, and H‐IL.…”

Dynamic solvent effects on the thermal isomerization of zinc dithizonate

“…The plots are linear and their b values (0.46-0.53) are smaller than 1 as expected for the viscosity dependence of the fluctuation-limited rate process. 26,29,30,[33][34][35][36] In the nonpolar and highly-viscous solvent DCMP as shown in Fig. 2, the pressure-induced retardation is more pronounced compared to that in GTA (Fig.…”

“…Therefore, high-pressure kinetics in highly viscous solvents are of considerable interest to study how the solvent molecules are involved in the activation step. 29,30 In this study, we examined pressure and temperature effects on the thermal isomerization of zinc dithizonate (Zn(HDz) 2 ) in low-and high-viscosity solvents in order to investigate the role of dynamic solvent effects on this isomerization. A large, pressure-induced retardation of this isomerization in highlyviscous solvents was observed, which suggested the presence of dynamic solvent effects and invalidated the TST.…”

Dynamic solvent effects on the fading of a merocyanine formed from a spironaphthoxazine. A case of a strong coupling between chemical and medium coordinate

“…In previous papers, [1][2][3][4][5] we reported results of kinetic measurements on isomerizations of organic molecules at highly viscous conditions where solvent reorganization was a rate-controlling factor. The purpose of studies of such unusual kinetics was to derive information on the extent of coupling between solvent reorganization and chemical structural changes during the activation step.…”

“…At least a two-dimensional potential energy surface (PES) with one dimension for solvation changes and the other for chemical structural changes of the reactant 19 was required. [1][2][3][4][5] As part of our efforts to examine the limits of the validity of this conclusion, we extended our measurements to the reaction of fading of a merocyanine…”