Understanding the Photoexcitation of Room Temperature Ionic Liquids

Abstract

Photoexcitation of (neat) room temperature ionic liquids (RTILs) leads to the observation of transient species that are reminiscent of the composition of the RTILs themselves. In this minireview, we summarize state‐of‐the‐art in the understanding of the underlying elementary processes. By varying the anion or cation, one aim is to generally predict radiation‐induced chemistry and physics of RTILs. One major task is to address the fate of excess electrons (and holes) after photoexcitation, which implies an overview of various formation mechanisms considering structural and dynamical aspects. Therefore, transient studies on time scales from femtoseconds to microseconds can greatly help to elucidate the most relevant steps after photoexcitation. Sometimes, radiation may eventually result in destruction of the RTILs making photostability another important issue to be discussed. Finally, characteristic heterogeneities can be associated with specific physicochemical properties. Influencing these properties by adding conventional solvents, like water, can open a wide field of application, which is briefly summarized.

Chemistry Dissolved in Ionic Liquids. A Theoretical Perspective

“…It is worth mentioning that excess electrons , in ionic liquids have been studied from AIMD simulations as well. As Unterreiner and co-workers point out, a major task is to understand “the fate of excess electrons (and holes)”, which needs the consideration of “various formation mechanisms considering structural and dynamical aspects” . Wang et al investigated an excess electron in eight ion pairs of 1-methylpyridinium chloride already in 2010 .…”

“…31,32,121,122 To be able to study the complicated electronic structure of such systems in ILs, they specifically developed a spin ratio scaled MP2 method termed SRS-MP2. 123 It is worth mentioning that excess electrons 124,125 in ionic liquids have been studied from AIMD simulations as well. As Unterreiner and co-workers point out, a major task is to understand "the fate of excess electrons (and holes)", which needs the consideration of "various formation mechanisms considering structural and dynamical aspects".…”

“…As Unterreiner and co-workers point out, a major task is to understand "the fate of excess electrons (and holes)", which needs the consideration of "various formation mechanisms considering structural and dynamical aspects". 125 Wang et al investigated an excess electron in eight ion pairs of 1methylpyridinium chloride already in 2010. 126 While they used the generalized gradient approximation (GGA) functional BLYP 127,128 to generate the trajectory, they added calculations employing exact exchange density functionals on top of these simulations at certain snapshots of the BLYP trajectory.…”

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

“…Additionally, ILs can act as the species absorbing photons themselves, and their behavior after photoexcitation has been investigated. 1895 Homogeneous photocatalytic systems are primarily associated with the reduction of CO 2 (CO 2 RR), although there are only a few examples available. On the other hand, ILs have been extensively utilized in heterogeneous photocatalysis, particularly in the synthesis of semiconducting materials.…”

“…In homogeneous systems, ILs can serve as quenchers of the excited state of a photosensitizer, transferring the resulting radicals to other species. Additionally, ILs can act as the species absorbing photons themselves, and their behavior after photoexcitation has been investigated . Homogeneous photocatalytic systems are primarily associated with the reduction of CO 2 (CO 2 RR), although there are only a few examples available.…”