Optical properties of irradiated imidazolium based room temperature ionic liquids: new microscopic insights into the radiation induced mutations

Abstract

Considering the future perspectives of room temperature ionic liquids (RTILs) in areas involving high radiation fields (such as the nuclear fuel cycle and space applications), it is essential to probe and have a microscopic understanding of the radiation induced perturbations in the molecular structures and the intrinsic bonding interactions existing in the ILs. Herein, a focused investigation concerning the photophysical behavior of post-irradiated FAP (fluoroalkyl phosphate) imidazolium ILs revealed considerable rearrangements and bonding realignments of the ionic moieties in the ILs on irradiation, however, their physicochemical properties do not change significantly even at high absorbed doses. Most interestingly, the well-established excitation wavelength dependent fluorescence (FL) behavior of the ILs was considerably perturbed on irradiation and this is attributed to the radiation induced decoupling of pre-existing different associated structures of ions, and the subsequent formation of oligomers and other species containing multiple bond order groups. This was further substantiated by vibrational studies, where peaks appearing in the range 1600-1800 cm(-1) indicated the formation of double bonded products. Furthermore, for the hydroxyl functionalized (in the alkyl side chain of the imidazolium cation) IL, a blue shift in the O-H stretching frequency was observed for the -OH group H-bonded to the FAP anion (νOH···[FAP](-)), while a red shift was observed for the H-bonded -OH groups in the cationic clusters. The FL lifetime values were found to increase with irradiation, which clearly indicates the enhancement in the rigidity level in the vicinity of the ions, thereby hindering the non-radiative decay processes. Such studies could contribute to the fundamental understanding of the radiation driven perturbations in the structure-property relationships, which eventually affect the radiolytic degradation pathways and the product distribution in RTILs.

Size Tuning, Phase Stabilization, and Anticancer Efficacy of Amorphous Selenium Nanoparticles: Effect of Ion-Pair Interaction, −OH Functionalization, and Reuse of RTILs as Host Matrix

“…The color appearance (pale orange) in post-irradiated neat RTILs (Figure d–f) is an indication of their radiolytic degradation. It should be noted that several studies in the recent past have clearly reported a high radiation stability of imidazolium-based RTILs, and a degradation of only 1 mol% (or less) has been observed even at high absorbed doses of up to 500 kGy. ,,,− This can be envisaged from the minimal (or negligible) variations in the FTIR spectra of pre- and post-irradiated RTILs, as shown in Figure S2. However, the color evolution in post-irradiated RTILs has been attributed to the formation of oligomeric and multiple bond order products (having a high molar extinction coefficient). − …”

Tuning Intercrystalline Void-like Defects in Nanowire Clusters to TiO2 Quantum Wires with Enhanced Photocatalytic Performance

“…The dissociation of secondary crystals originating from localized regions of the parent structure adopts a mechanism of assembly assisted by the more stable cationic imidazolium ring clusters in intercalated arrangements at the solid–liquid interface of organometallics . This conclusion is supported by large C–H stretching frequencies assigned to the imidazolium C 5 N ring configuration or associated alkyl moieties at 1088 cm –1 and 1323 cm –1 (Figure ) associated with sizable C–N asymmetric vibrations that extend from 1066 to 1130 cm –1 (Figure ). The low temperature binding functionality of the imidazolium ring in SMoQWs is better resolved at the interfacial surfaces as judged from the FTIR spectral bond vibration between the positively charged imidazolium moieties and the carboxylate groups at the TiO 2 surface at 1171 cm –1 (Figure ), revealing a sharp spectral band between surface carboxylates (COO̅) and protonated N + of the EMIM ring clusters.…”

γ-Radiolysis of Room-Temperature Ionic Liquids: An EPR Spin-Trapping Study

“…There are numerous investigations of changes in the physical properties of ILs during radiolysis, such as viscosity, density, conductivity, and optical absorbance. − Mass spectroscopy and nuclear magnetic resonance (NMR) have been used to identify products and degradation of the starting IL after irradiation with large doses. ,,, Radiation-induced degradation of ILs at lower dose can be quickly assessed by an analysis of the yields of gas generated in radiolysis, among which hydrogen is the main product. − In our previous study, we analyzed the yields of gaseous hydrogen formed during radiolysis of several RTILs with bis­(trifluoromethylsulfonyl)­imide anion and identified that aromatic imidazolium and pyridinium ILs gave the smallest G (H 2 ) yield . The radiolytic free-radical mechanism in ILs is mainly quantified by measuring the yields of the transients formed in pulse radiolysis with transient optical absorbance. − A large number of papers are devoted to studies of solvated electron yields and kinetics in a wide range of ILs. − Shkrob and co-workers used continuous wave electron paramagnetic resonance (cw-EPR) spectroscopy to detect radical intermediates generated from frozen ILs upon exposure to ionizing radiation at low temperature. ,− They found that ILs consisting of aromatic heterocyclic ions exhibit better radiation and electrochemical stability because of their extended conjugated bonds.…”