DUAL INFLUENCE OF H-BONDING ON THE SOLID-STATE 2ND-HARMONIC GENERATION OF A CHIRAL QUINONOID COMPOUND

A new chiral push-pull quinonoid compound, 3(R)-hydroxypyrrolidino)-8, 8-dicyanoquinodimethane (BHPDQ), has been synthesized. Powder studies indicate an appreciable second harmonic generation (SHG) capability, a nd crystal structure analysis reveals extensive intermolecular H-bondi ng in BHPDQ. The influence of H-bonding and molecular chirality on the dipole alignment in the crystal is described. The H-bonds play an unu sual role of modifying the molecular structure by producing an enhance d molecular twist in BHPDQ; this in turn affects the molecular hyperpo larizability. Thus we describe a novel instance wherein the powder SHG in a molecular material is determined by the dual influence of interm olecular H-bonding on the crystal structure as well as on the molecula r structure and hyperpolarizability. The new dimension that this obser vation adds to the general theme of molecular materials design is high lighted.