Solvent Role of Ionic Liquids in Fundamental Chemical Reaction Dynamics Analyzed by Time‐Resolved Spectroscopy

Abstract

Ionic liquids (ILs), which are used as solvents for chemical reactions, are different from conventional organic solvents owing to their designability. Physicochemical parameters of the ILs, such as polarity and viscosity, that affect chemical equilibria and reaction kinetics can be tuned by changing the combination of anions and cations or by varying the lengths of the alkyl chains present in the cations. We were interested in knowing how these physicochemical parameters affect fundamental chemical reactions in ILs. Therefore, in this personal account, we investigate our recent work on two different photochemical reactions in ILs, namely excited‐state intramolecular proton transfer of hydroxyflavone and photodissociation of aminodisulfide, using time‐resolved spectroscopic techniques. Interestingly, the roles of the ILs in these chemical reactions are quite different. The effect of the cationic species of the ILs (i. e., the head groups and number of alkyl carbons) on the solvation environment upon photoexcitation and reaction rate are discussed.

Anion Effect on the Excited-State Intramolecular Proton Transfer of 4′-N,N-Diethylamino-3-hydroxyflavone in Ionic Liquids

“…Ionic liquids (ILs) are known to provide a heterogeneous solvation environment depending on the choice of cations and anions. In particular, ILs with cations having long alkyl chains show a segregated structure of polar and nonpolar domains due to the existence of both charged polar and nonpolar alkyl parts in the cation. − Various unique solvation phenomena have been reported due to the existence of the heterogeneous structure. − The excited-state intramolecular proton transfer (ESIPT) reaction of 4′- N,N -diethylamino-3-hydroxyflavone (C 2 HF) is an interesting example (Figure ). − C 2 HF exists as a normal form (keto form) in the electronic ground state.…”