Spectroscopic Study on Imidazolium-Based Ionic Liquids: Effect of Alkyl Chain Length and Anion

Abstract

Room temperature ionic liquids are currently used as functional materials in several application and their optical investigation can provide a better understanding of their physical and chemical behavior. Absorption and emission properties of imidazolium-based ILs have been attributed to the imidazolium moiety and related to the presence of energetically different aggregates. Here, time-integrated and time-resolved investigation has been carried out on 1-alkyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids with different chain lengths in order to probe the occurrence of energy transfer processes, and hence to disclose the presence of various states with different energy. Such a study contributes to provide relevant insight on the effect of alkyl chain and anion type on the emission characteristics, and, hence, on the presence of associated structures.

Photostability and photocatalytic degradation of ionic liquids in water under solar light

“…Additional 43,44 In addition, several works demonstrated that those different ionic species are responsible of in the complex photophysical properties of ILs in solution. 45,46 Then, current simulations involve "independent ions" and "ion-pair" molecular models (see Fig. S2 in ESI †).…”

Poly(4-vinylpyridine) as ligand for Au(I) and Zn(II) cations: luminescent metal-containing polymers

“…Like pyridinium, the imidazolium cation is a six-electron π system. The unusual luminescence properties have been explained by the existence of aggregated species which give rise to energetically different excited (and emissive) states with inefficient excitation energy-transfer process between them [51][52][53][54]. In an analogous interpretation, the zinc cations in P4VP might impose aggregation of pyridine chromophores.…”

Nanocomposites Based on Luminescent Colloidal Nanocrystals and Polymeric Ionic Liquids towards Optoelectronic Applications

“…In the UV spectral region, both the colloidal NCs and the imidazolium-based PILs absorb. The absorption of the CdSe NCs is due to the continuum of the states typical of semiconductors, while that of the PIL solution in DMSO is ascribed to π–π* transitions of the imidazolium ring [ 35 , 36 ]. The tail, which instead appears in the spectra of the PIL in the visible range, can be ascribed to the presence of energetically different associated structures, originated from strong interactions among the π delocalized orbitals of the imidazolium ring [ 35 , 36 ].…”

“…The absorption of the CdSe NCs is due to the continuum of the states typical of semiconductors, while that of the PIL solution in DMSO is ascribed to π–π* transitions of the imidazolium ring [ 35 , 36 ]. The tail, which instead appears in the spectra of the PIL in the visible range, can be ascribed to the presence of energetically different associated structures, originated from strong interactions among the π delocalized orbitals of the imidazolium ring [ 35 , 36 ]. Nevertheless, due to the high absorption between 500 and 650 nm, the presence of some residual impurities originating from the synthetic procedure of the IL and/or from halide ions preceding the anion exchange in the PIL synthesis cannot be ruled out [ 37 , 38 ].…”