Ultrafast Formation of a Three-Electron-Bonded Radical Anion (CH₃S∴SCH₃^-) in a Liquid Organic Sulfur Compound

Abstract

The elementary steps of an electron photodetachment triggered by the UV excitation of pure liquid dimethyl sulfide, (CH3)2S, have been investigated by femtosecond absorption UV−IR spectroscopy at 294 K. The buildup of a long-lived UV band centered around 420 nm (3.26 eV) is observed at the sub-picosecond time scale. This spectral band is assigned to a radical anion (CH3S∴SCH3 -) characterized by a sulfur−sulfur bond with an antibonded third electron (2c, 3e). A very short-lived electronic state, whose rise time equals 180 ± 10 fs, exhibits a spectral overlap with this UV radical. The frequency and time dependences of induced absorption signals are analyzed in the framework of a kinetic model for which an early electron transfer yields an ultrashort-lived anion radical ({RSR-}RSR or R = CH3). The decay rate of this UV state (1/τ = 3.7 × 1012 s-1) is rationalized by postulating an ultrafast ion−molecule reaction and the picosecond formation of a disulfide radical anion (CH3S∴SCH3 -) characterized by a 2σ/1σ* bond. A second electron-transfer channel leading to a delayed formation of a disulfide anion radical (RS∴SR-) has been identified by time-resolved IR spectroscopy. These femtosecond investigations argue for an ultrafast formation of a sulfur−sulfur bond with C−S bonds breaking. It is suggested that the density-state fluctuations of organic sulfur molecules influence the energy of early electron−thioether couplings (electron attachment or localization) and would govern competitive branchings between ultrafast electron photodetachment channels.

Ultrafast Decay of the Solvated Electron in a Neat Polar Solvent: The Unusual Case of Propylene Carbonate

“…The behavior of PC is then very similar to that of dimethylsulfide. 26,27 In the competition between solvation or attachment of the electron in the presence of PC molecules, our results indicate that the reactivity of the solvated electron with the solvent molecule is moderate and less efficient. This is in line with the value of the measured rate constant k(e PC − + PC) = 1.9 × 10 8 L mol −1 s −1 , which is much lower than a diffusion controlled process.…”

“…15 A third case is that the solvated electron and the radical anion are produced simultaneously as in dimethylsulfide. 26,27 In polar solvents, the electron radiolytic yield at a few tens of picoseconds (G t (e PC − )) is generally about 4 × 10 −7 mol J −1 . 28−30 Knowing that G t (e PC − ) × ε λ = A λ,t /(D × ρ × l), where ε λ is the molar extinction coefficient in L mol −1 cm −1 of the solvated electron, A λ,t is the measured absorbance, D is the dose (in J kg −1 ), ρ is the density of the solution, and l is the optical path in cm, the molar absorption coefficient of e PC − at 50 ps would be ε 1310 nm (e PC − ) (50 ps) = 3300 L mol −1 cm −1 .…”

Interactions of Amino Acids with Oxidized Guanine in the Gas Phase Associated with the Protection of Damaged DNA

“…[45] Previous reports indicate that the existence of radical with a 2c-3e bond can be observed by its UV signal. [46] Thus, time-dependent DFT (TD-DFT) [47] calculations were performed to examine the excitation wavelength which corresponds to the transition of an electron from a doubly occupied bonding orbital to the singly occupied antibonding orbital (s!s*) for the 2c-3e-bonded complexes with the optimized geometries. Electronic absorption spectra were generated by the Swizard program, revision 4.5, [48] using the Gaussian model.…”

Redox‐induced configuration conversion for thioacetamide dimer can function as a molecular switch

“…Binding energies* between the two fragments for the studied systems were determined with the basis set superposition error (BSSE) correction30, 31 and the zero‐piont energy correction. From the available data in the literature, the presence of a three‐electron bond (2σ/1σ*) is generally characterized by a UV‐IR spectral signature 32–35. So the time‐dependent density functional response theory (TD‐DFT)36 calculations were performed to find out the excitation wavelength to excite an electron from a doubly occupied bonding orbital to the lowest singly occupied antibonding orbital (σ→σ*) of the 2c‐3e bonded complexes with the optimized geometries.…”