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, -CH3, -CF3) on the hydrazone group (-CX = N-NH-) has been synthesized and their polymorphs have been investigated. The chromophore 2-((2-(4-nitrophenyl)hydrazono)methyl)-1H-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 mu m for the anisotropic polar HNPH-I with P-n space group and the isotropic nonpolar HNPH-II polymorph with P2(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.