Electron Photodetachment from Iodide in Ionic Liquids through Charge-Transfer-to-Solvent Band Excitation

Abstract

Solvation of iodide and electrons in an ionic liquid (N,N,N-trimethyl-n-propylammonium bis(trifluoromethanesulfonyl)imide; TMPA-TFSI) was studied through the absorption spectra of the charge-transfer-to-solvent (CTTS) state of iodide and of solvated electrons. The interaction between the TMPA cation and iodide was strong, whereas electrons were weakly solvated in TMPA-TFSI. We followed electron photodetachment from iodide to the ionic liquid and formation of the solvated electrons by observing absorption in the visible and near-infrared regions using a nanosecond laser flash photolysis method. The quantum yield of the photodetachment in TMPA-TFSI was estimated to be 0.34, which is much higher than that in a high-concentration aqueous salt solution previously reported. We also examined a reaction of the solvated electrons with the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (Bmim-TFSI) as a solute in TMPA-TFSI. The reaction rate was determined to be 5.3 x 10(8) M(-1) s(-1). The electrons before full solvation (dry electrons) reacted with Bmim cations efficiently. These observations suggest that the electrons in TMPA-TFSI can move easily before solvation.

Reactions of solvated electrons with imidazolium cations in ionic liquids

“…The absorption maxima are located at 1100 nm in all ionic liquids studied, which are similar to that observed in TMPA-TFSI as previously reported (Katoh et al, 2007). The similarity of the peak position implies that electrons in these ionic liquids are located in sites having similar chemical environments.…”

“…We have recently studied solvated electron in trimethyl-propylammonium-bis(trifluoromethylsulfonyl)imide (TMPA-TFSI) produced by pulse radiolysis as well as photodetachment of iodide through charge-transfer-to-solvent (CTTS) band excitation (Katoh et al, 2007). The spectra obtained from the both methods were identical and broad absorption band peaking around 1100 nm.…”

Ortho-Positronium Annihilation in Room Temperature Ionic Liquids

“…At first, the smaller S values at very young positron ages were explained by the slower Ps formation [7] by referring the report indicating the excess electrons move freely for longer time [4]. However, detailed analysis of AMOC results, i.e.…”

“…Some researches indicated that the excess electrons in room temperature ionic liquids (RTILs) move freely for relatively long time [4].…”

Reactions of excited-state benzophenone ketyl radical in a room-temperature ionic liquid

“…28 Many fast bimolecular reactions have been studied in ILs. [29][30][31][32][33][34][35][36][37] In general, hydrodynamic approximation of the diffusion coefficient on the basis of the Stokes-Einstein equation is not applicable to diffusion-limited reactions in ILs. Several research groups have suggested that the faster translational diffusion in ILs is due to a large void volume produced by cations and anions.…”