Substituent Effects on the Structural Features and Nonlinear Optical Properties of the Organic Alkalide Li+(calix[4]pyrrole)Li-

The effects of substituents on the structure, character, and nonlinear optical (NLO) properties of the organic alkalide Li+(calix[4]pyrrole)Li were studied by density functional theory. Natural bond orbital analysis and vertical ionization energies reveal that electron-donating substituents strengthen the alkalide character of Li+(calix[4]pyrrole)Li and that they are beneficial for a larger first hyperpolarizability (0) value. However, electron-withdrawing substituents have the opposite effect. The dependence of the NLO properties on the number of substituents and their relative position was detected in multisubstituted Li+(calix[4]pyrrole)Li compounds. For both the amino- and methyl-substituted derivatives, the polarizabilities and the first hyperpolarizabilities increase as more pyrrole -H atoms are substituted. Moreover, distribution of the substituents so that they are as far away from each other as possible resulted in an increase in the 0 value. The new knowledge obtained in this study may provide an effective approach to enhance the NLO responses of alkalides by employing pyrrole derivatives as complexants.