Effect of Hydrogen Bond on Second-Order Nonlinear Optical Property of 2-Alkylcarboxamido-4′-methoxy-4-nitrotolan Derivatives

We have synthesized a series of 2-alkylcarboxamido-4′-methoxy-4-nitrotolan derivatives and studied the second-order nonlinear optical properties using the total reflection technique. We measured the infrared absorption spectra of the derivatives and examined the absorption peak of the N–H stretching vibration around 3300 cm−1, which is sensitive to hydrogen bonding. We observed that the peak frequencies of the nonlinear optical active materials were lower than those of the inactive ones, and thus found that for 2-alkylcarboxamido-4′-methoxy-4-nitrotolan derivatives the hydrogen bond plays an important role in activating the second-order optical nonlinearity of the material.