Pyrrole-Based Hydrazone Organic Nonlinear Optical Crystals and Their Polymorphs

A series of new organic nonlinear optical nitrophenylhydrazone crystals based on pyrrole with various substituents (X: -H, -CH 3, -CF 3 ) on the hydrazone group (–CX═N–NH–) has been synthesized and their polymorphs have been investigated. The chromophore 2-((2-(4-nitrophenyl)hydrazono)methyl)-1 H -pyrrole (HNPH) exhibits two polymorphs with large macroscopic nonlinearity, with a powder second harmonic generation activity of 420 times and 210 times that of urea at 1.9 μm for the anisotropic polar HNPH-I with Pn space group and the isotropic nonpolar HNPH-II polymorph with P 2 1 2 1 2 1 space group, respectively. The microscopic and macroscopic nonlinearities in the crystallographic system have been analyzed theoretically using finite field calculations.