Theoretical study of the second-order nonlinear optical properties of ionic liquids

The second-order nonlinear optical properties of ionic liquids formed by [EMIM]+, [BMIM]+, [MePyrr]+, and [BuPy]+ cations in conjunction with four anions, [BF4]−, [NO3]−, [CF3COO]−, and [PF6]−, were carried out at the framework of the Density Functional Theory. First, we determine the first hyperpolarizability for all ions and later, we study the local interactions between the ions to find the key factor that determines their nonlinear optical properties of ionic liquids. The results show that [BuPy]+[CF3COO]−, [BuPy]+[NO3]−, [BuPy]+[BF4]−, and [BMIM]+[NO3]− systems have large first hyperpolarizabilities and can be treated as a good candidate for nonlinear optical devices.