SYNTHESIS AND X-RAY STUDIES OF NONCENTROSYMMETRIC MEROCYANINE DYES - A SERIES OF ORGANIC NLO CRYSTALS

A series of 3-methyl-4-(p'-substituted styryl) pyridine methiodides we re readily synthesized under mild condition with excellent yields. The 3-methyl group was expected to direct the molecular packing within th e crystalline unit cell. X-ray diffraction analysis of 3-methyl-4-styr ylpyridine methiodide crystal clearly showed that this compound was pa cked in a noncentrosymmetric way about 50 degrees with respect to the crystal polar axis, and proved that the 3-methyl group on pyridine rin g did change the molecular packing from centrosymmetric orientation to noncentrosymmetric orientation. However, all other compounds we inves tigated in this paper were found crystallized centrosymmetrically.