Wl. Chia et al., SYNTHESIS AND X-RAY STUDIES OF NONCENTROSYMMETRIC MEROCYANINE DYES - A SERIES OF ORGANIC NLO CRYSTALS, Materials research bulletin, 30(11), 1995, pp. 1421-1430
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.