SHG-active polymorphism of p-nitroaniline mixed with its N-alkyl derivatives

The second-harmonic generation (SHG) in each mixture of p-nitroaniline (p-NA) and its derivatives (n-methyl, n-ethyl, n-propyl, i-propyl, n-butyl, n-hexyl, dimethyl, phenyl, and diethyl-4-nitroaniline) was measured by the powder method with a Nd:YAG laser. Most of the mixtures having a typical eutectic phase diagram exhibited a high SHG intensity; in particular, the SHG activity of the p-NA/isopropyl-NA mixture was 1670 times higher than that of urea. This may be due to the crystal growth of noncentrosymmetrical polymorphism of p-NA on the surface of the isopropyl-NA. The crystal growth of the SHG-active polymorphism was accomplished by vacuum deposition on the isopropyl-NA substrate.