Electron photodetachment from iodide in ionic liquids through charge-transfer-to-solvent band excitation

Kato, Ryuji*; Yoshida, Yoichi*; Katsumura, Yosuke; Takahashi, Kenji*

Solvation of iodide and electrons in an ionic liquid (-trimethyl--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, where as 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 5.310 Ms. 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.