Tuning the nonlinear optical properties of the [alkyl-Py]+[NO3]- and [alkyl-MIM]+[NO3]- ionic liquids

A series of ionic liquids composed of 1-butyl-, 1-hexyl-,1-octyl-, and 1-Tenyl-pyridinium and 1-butyl-, 1-hexyl-, 1-octyl- and 1-Tenyl-3-methylimidazolium cations with the anion nitrate were investigated using the Density Functional Theory. The systematic analysis of several nonlinear optical properties was performed in order to determine the relation between them and the alkyl chain length. The calculations indicate that the first hyperpolarizabilities of both groups increase as the alkyl chain length spreads, being these values higher than the urea value which is a typical molecule used to study the NLO properties. Our findings allow us to propose these ionic liquids as good candidates for the development of nonlinear optical devices. (C) 2019 Published by Elsevier B.V.