Investigation of solvent dynamic effects on the electron self-exchange in two thianthrene couples with large inner reorganization energies

Abstract

The large structural difference between thianthrene radical cations and their neutral parent molecules can possibly affect their electron self-exchange reactions. Before this can be investigated experimentally, it is necessary to first understand the influence of the solvent on such electron transfer reactions. To achieve this, the rate constants of the electron self-exchange reactions of the Th˙(+)/Th and MTh˙(+)/MTh (Th = thianthrene, MTh = 2,3,7,8-tetramethoxythianthrene) couples were investigated by means of ESR line broadening experiments in different solvents at 293 K. The diffusion corrected rate constants cover a range of 7.2 × 10(8)≤ket≤ 44 × 10(8) M(-1) s(-1) for Th˙(+)/Th and 2.0 × 10(8)≤ket≤ 11.6 × 10(8) M(-1) s(-1) for MTh˙(+)/MTh, respectively. The results were analysed within the framework of the Marcus Theory and the characteristic reorganization energy, λ, was determined. Both couples clearly show a solvent dynamic effect controlled by the longitudinal relaxation time τL of the solvents. However, the influence of the structural changes, in terms of λ, was smaller than expected at room temperature.

Organic Solvent Effects in Biomass Conversion Reactions

“…If the reaction is largely controlled by static effects, the solvent's relaxation is fast compared to the activation process and the activated complex is largely in thermal equilibrium with the solvent. However, this equilibrium assumption is usually not valid for a chemical reaction in a strongly dipolar and/or slow‐relaxing solvent . In this situation, rate constants will depend on solvent dynamics and will vary with parameters that include density, internal pressure, or viscosity.…”

“…However,t his equilibrium assumption is usually not valid for ac hemical reactioni nastrongly dipolar and/or slow-relaxing solvent. [141][142][143][144][145][146][147][148] In this situation, rate constants will depend on solventd ynamics and will vary with parameters that include density,i nternal pressure, or viscosity.E speciallyf or rapid chemicalr eactions, the slow relaxation of the solvent will affect the activation process. In such cases, the activation process can be limited by the time taken by molecules to reorient themselves around the transition state.…”

The use of a tertiary solvent mixture to study solvent dynamic effects in the photoinduced electron transfer reaction of excited singlet pyrene and indole

“…18 The electron transfer rate constant, k et , is solvent-dependent in several terms. The pre-exponential factor depends on the nature of the solvent via the solvent reorganization energy l 0 [22][23][24] and, of course, the solvent reorganization energy, l 0 is expressed by the solvent refractive index n and its dielectric constant e s . In addition, k q depends on the solvent viscosity and finally the resonance splitting energy V PS is assumed to be refractive index dependent.…”

Influence of the medium's viscosity on the kinetics of hydrogen atom self-exchange for N-hydroxy phthalimide/piperidine-N-oxyl (NHPI/PINO˙) measured by CW-ESR spectroscopy

“…This type of experiment was introduced in the 1950s 18 to study electron self-exchange reactions and is currently used in this field. [19][20][21] To our knowledge we report the first successful CW-EPR line broadening experiment to obtain kinetics of a real hydrogen atom self-exchange with DG1 = 0. PINO is prone to selfdecomposition, with a lifetime of minutes.…”