Structure and Nonlinear Optical Characterization of a New Acentric Crystal of a 4-Hydroxybenzohydrazide Derivative

We report the crystal structure and nonlinear optical (NLO) characterization of the monohydrate form of N′-[(E)-(2-fluorophenyl)methylidene]-4-hydroxybenzohydrazide (o-FHH), an organic compound showing strong potential for second-order nonlinear optical applications. The compound crystallizes in a non-centrosymmetric tetragonal space group. The supramolecular features of the novel crystal structure are strongly related to the role of the water molecule that stabilized columns of o-FHH through strong hydrogen bonding interactions. This structural feature is reflected in the high thermal stability of the compound, which is evidenced by its ability to withstand temperatures in excess of 100 ◦C without losing the water molecule. Second-harmonic generation (SHG) imaging confirms bulk nonlinearity throughout the entire volume of the crystal, consistent with the acentric class of the novel compound. The combination of a dense hydrogen-bonding network, structural robustness, and the ability to grow millimeter-sized single crystals makes o-FHH a good candidate for further development as an organic NLO material.