Competition between Geminate Recombination and Solvation of Polar Radicals following Ultrafast Photodissociation of Bis(p-aminophenyl) Disulfide

Abstract

Supercontinuum probe pulses are used for studying the ultrafast photodissociation of bis(p-aminophenyl) disulfide into two p-aminophenylthiyl radicals and their subsequent geminate recombination in polar solvents. The kinetic investigations are complicated by a spectral absorption shift of the photolytically generated radicals due to solvation. The dissociation and recombination dynamics are separated from the solvation dynamics by a moment analysis of the transient spectra. Geminate recombination in polar solvents is observed only if the time scale for dielectric relaxation of the solvent is comparable to or slower than the time scale for recombination. The latter depends on the initial distance distribution of the radical pairs.

Photochemical reaction dynamics of 2,2′-dithiobis(benzothiazole): direct observation of the addition product of an aromatic thiyl radical to an alkene with time-resolved vibrational and electronic absorption spectroscopy

“…photolytically from bis(p-aminophenyl)disulfide using a geminate recombination model. 14 According to the model, the survival probability Φ(t) is described by:…”

“…13 Photodissociation of aromatic disulfide systems on sub-picosecond time scales was intensively explored in the late 1980s and 1990s. [14][15][16][17][18] Scott et al investigated the simplest aromatic disulfide, diphenyl disulfide in the liquid phase and focused on geminate recombination dynamics of the resulting phenylthiyl radical by applying a diffusion model. 18 Lochschmidt et al examined the photodissociation dynamics of bis(julolidine) disulfide in both polar and apolar solvents, and observed rapid formation of julolidylthiyl radicals within 130 fs and subsequent geminate recombination of the radicals, as well as production of a radical dimer.…”

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

“…42 The calculated rate coefficient also incorporates the formation of a QS radical dimer, as discussed further below. This model was employed by Bultmann et al for analysis of the cage recombination dynamics of p-aminothiophenoxy radicals generated photolytically from bis(p-aminophenyl)disulfide, 10 as well as in our previous report on the photochemical reaction dynamics of another aromatic disulfide. 9 The details of our fitting method and interpretation of the biexponential decays are provided in the Supplementary Information and Figure S6.…”

“…5,6 Thiol-ene reactions proceed via reaction steps (i)  (iii), but also potentially include other reaction steps (iv)  (vii), which result in side-products: 6,7 Light irradiation or radical initiators can be used to produce thiyl radicals (step (i)), but the former method involving photodissociation of the corresponding thiol (as shown in (i)) or disulfide is preferred for the study of their mechanisms and dynamics because of the almost instantaneous (sub-picosecond) formation of thiyl radicals. [8][9][10] The photodissociation dynamics producing aromatic thiyl radicals have mostly been deduced from studies using transient electronic absorption spectroscopy (TEAS), [8][9][10][11][12][13][14][15][16][17] because aromatic thiyl radicals show strong absorption bands in the ultraviolet (UV) and visible regions. 6 The mechanisms of addition of thiyl radicals to alkenes (or alkynes), which yield carbon centered radicals (step (ii)), were extensively investigated by Ito et al in the 1980s using a microsecond flash photolysis method, and have been reviewed previously.…”

The roughness of the protein energy landscape results in anomalous diffusion of the polypeptide backbone

“…This theoretical prediction has been shown experimentally to be valid for the geminate recombination of aromatic thiyl radicals in solution. 111,115 The instantaneous rate constant k inst (t) = À(dP(t)/dt)/P(t) can be easily calculated from this expression. Fig.…”