Role of Metal Ions(M=Li~+,Na~+,and K~+)and Pore Sizes(Crown-4,Crown-5,and Crown-6)on Linear and Nonlinear Optical Properties:New Materials for Optical Birefringence

摘要

Density functional theory(DFT)calculations are performed on Li~+,Na~+,and K~+ complexes of crown-4,crown-5,and crown-6,respectively.Calculations show that,for all three structures,the rings are puckered to maintain the staggered conformations along the C-C dihedral angles.The Li~+,Na~+,and K~+ are deflected from the center-of-mass of the crown ethers by 0.82,0.98,and 0.33 A,respectively,toward the surface more exposed to O atoms.These M~+ complexes have different linear(a)and nonlinear(beta)polarizations on the top and bottom surfaces for equal distortions on either surface.The variation in alpha and beta is also studied with respect to the movement of the cations along the pore of the crown ether.The inherent asymmetry in the in-plane(alpha_(ip))and out-of-plane(alpha_(op))components of the polarizations leads to a single-humped profile of optical birefringence with respect to the motion of the M~+ ion along the pore.Our calculations show that the optical birefringence for these molecules,in their equilibrium geometry,is very close to their maximum possible theoretical limit.