Twin-peaks absorption spectra of excess electron in ionic liquids

The solvated electron in room temperature ionic liquids (RTILs) has been the subject of several investigations and several reports exist on its nature and absorption spectrum. These studies concluded that the solvated electron exhibits an absorption spectrum peaking in the 1000–1400 nm region; a second absorption band peaking in the UV region has been assigned to the hole or dication radicals simultaneously formed in the system. Here we report on the fate of the excess electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, P₁₄⁺/NTf₂⁻ using nanosecond pulse radiolysis. Scavenging experiments allowed us to record and disentangle the complex spectrum measured in P₁₄⁺/NTf₂⁻. We identified a bi-component absorption spectrum, due to the solvated electron, the absorption maxima located at 1080 nm and around 300 nm, as predicted by previous ab-initio molecular dynamics simulations for the dry excess electron. We also measured the spectra using different ionic liquids and confirmed the same feature of two absorption peaks. The present results have important implications for the characterization of solvated electrons in ionic liquids and better understanding of their structure and reactivity. - Highlights: • The solvated electron (e_sol⁻) in the ionic liquids P₁₄⁺/NTf₂⁻ was investigated. • Pulse radiolysis shows a twin-peak absorption spectrum for the e_sol⁻ in P₁₄⁺/NTf₂⁻. • The absorption spectrum of the hole was measured using scavenging experiments