STRUCTURAL STUDIES OF A SERIES OF ORGANIC NONLINEAR-OPTICAL MATERIALS

The crystal structures of is(diethylamino)-methylium]phenyl}dicyanomet hanide (I), {4-[cyano(4-methylpiperidyl)methylium]phenyl} dicyanometha nide (II), o(1-pyrrolidinyl)methylium]phenyl}dicyanomethanide (IV) and iethylamino)-2-propenylium]phenyl}dicyanomethanide have been determin ed by X-ray crystallography. Together with iethylamino)-2-propenylium] phenyl}dicyanomethanide [(III): Cole, J. C., Howard, J. A. K., Cross, G. H. & Szablewski, M. (1995). Acta Cryst. C51, 715-718], these compou nds exhibit varying degrees of quinoidal characteristics and yet have predominantly zwitterionic ground state character. The presence of hig h dipole moments in the crystal can thus be inferred and are substanti ated by measurements of high solution-state dipole moments. Negative s olvatochromism (hypsochromism on increasing solvent polarity) confirms the zwitterionic character in at least two of the series.