Ultrafast transient absorption spectrum of the room temperature Ionic liquid 1-hexyl-3-methylimidazolium bromide: Confounding effects of photo-degradation

Abstract

The photochemistry of the charge transfer (CT) band of the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium bromide (HMIm + /Br-) is investigated using near-IR to Vis ultrafast transient absorption (TA) and steady-state UV absorption spectroscopies. Continuous irradiation of the CT band at 266 nm results in the formation of photo-products that absorb strongly at 266 nm. It is shown that these photo-products, which are apparently very stable, adversely affect ultrafast TA measurements. Elimination of these effects reveals at least two transient species that exist within the TA detection window of 100 fs to 3 ns and 500 nm to 1250 nm. One of the components is a short-lived (<1 ps) species that absorbs at 1080 nm. A second band exhibits a multicomponent spectrum that is very broad with an absorption maximum around 600 nm and a lifetime that is longer than the 3 ns window of our TA spectrometer. Within the signal to noise ratio of the TA spectrometer little to no solvated electron is generated by the CT mechanism.

Photodetachment and Electron Dynamics in 1-Butyl-1-methyl-pyrrolidinium Dicyanamide

“…The absorption spectra of excess charges in a variety of ionic liquids have been studied using pump-probe spectroscopy, pulsed radiolysis, and computational approaches. − The absorption across the visible and near-infrared (IR) appears bimodal, with peaks in both the visible and near-IR. Electron scavenging experiments and computational studies reveal that the broad, near-IR absorption feature peaked around 1.1 eV is due to the absorption of solvated free electrons. ,, Absorption in the visible region was assigned to the combined absorption of the hole and the free electron, with hole absorption dominating at higher energies. , …”

“…16,17,20 Absorption in the visible region was assigned to the combined absorption of the hole and the free electron, with hole absorption dominating at higher energies. 19,21 A number of prior studies have revealed and quantified the broad array of time scales exhibited in ionic liquids. The additional complexity of the multifaceted solvent time scales can have a substantial influence on the observed rates of bimolecular reactions.…”

High-Performance Rechargeable Aluminum–Selenium Battery with a New Deep Eutectic Solvent Electrolyte: Thiourea-AlCl3

“…8 In addition, the bromide-based electrolyte has lower photostability than that of the chloride-based electrolyte. 9,10 Therefore, it remains challenging to develop highperformance Al−S batteries. Selenium is a chemical analogue of sulfur, which is considered as an alternative cathode material in rechargeable lithium−ion and sodium−ion batteries 11−14 because of a much higher electronic conductivity (1 × 10 −3 S m −1 vs 5 × 10 −28 S m −1 ) and lower ionization potentials (9.7 eV vs10.4 eV), respectively.…”

Role of the Solvent–Surfactant Duality of Ionic Liquids in Directing Two-Dimensional Particle Assembly

“…Furthermore, studies show that the radiolytic species generated by e-beam, such as excess electrons, in pure aromatic IL are very short-lived (less than 1 ps lifetime) because they react quickly with the aromatic cations of IL. 21 In mixed IL/water/auric ion solutions, we expect that excess electrons will be partially captured by auric cations, thereby reducing the production of IL radicals. Moreover, the fact that, for intermediate concentrations of IL, the NPs assemble into an ordered array but remain separate despite the radiolytic effect on the water thus further highlights the critical role of the IL in acting as a surfactant to stabilize the array of individual particles.…”

“…In all in situ TEM experiments in this study, the accumulated dosage was around 10 –3 A/cm 2 and thus IL decomposition was unlikely. Furthermore, studies show that the radiolytic species generated by e-beam, such as excess electrons, in pure aromatic IL are very short-lived (less than 1 ps lifetime) because they react quickly with the aromatic cations of IL . In mixed IL/water/auric ion solutions, we expect that excess electrons will be partially captured by auric cations, thereby reducing the production of IL radicals.…”