Abstract
Nonlinear optical phenomena play significant roles in the bulk properties and responsive characteristics of ionic liquids, especially when used under strong electric fields. The variability of the anion-cation pair in ionic liquids makes them designer solvents; thus, the anion or cation dependency of the physicochemical properties should be understood in depth. Accordingly, the electric field-induced characteristics of eight ionic liquids with [Br]−, [BF4]−, [PF6]−, [Ac]−, [TFAc]−, [MS]−, [NTf2]−, and [Tos]− anions paired with the 1-butyl-3-methyl imidazolium cation were investigated using density functional theory modeling at four theoretical levels: B3LYP-6-31G(d), M06-2X 6-31G(d), M06-2X 6-311++G(d,p), and M06-2X aug-cc-PVTZ. The frontier molecular orbitals, electrostatic potential surface, and electron density difference maps were obtained to visualize the electrostatic characteristics. The permanent electric dipole moment, linear electric polarizability, and first-order and second-order hyperpolarizabilities were also determined. While the static dipole moment and dipole polarizabilities could be obtained using low-level quantum chemistry at a satisfactory level, the functionalization of more intensive methods was required to accurately obtain the nonlinear optical properties.
Published Version
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