Noncentrosymmetric Organic Solids with Very Strong Harmonic Generation Response

摘要

The molten reaction of 2-naphthol,4-(aminomethyl)pyridine,and 4-pyridinecarboxaldehyde at about 180 °C yields trans-2,3-dihydro-2,3-di(4'-pyridyl)benzo|V]indole (1)which possesses two chiral centers,rather than an expected Betti-type reaction product with only one chiral carbon center.The same reactions,using 3-pyr-idinecarboxaldehyde,4-cyanobenzalde-hyde,or 3-cyanobenzaldehyde instead of 4-pyridinecarboxaldehyde produce the related compounds trans-2,3-dihy-dro-2-(4/-pyridyl)-3-(3"-pyridyl)benzo-[e]indole (2),trans-2,3-dihydro-2-(4'-pyridyl)-3-(4"-cyanophenyl)benzo[>]in-dole (3),and trans-2,3-dihydro-2-(4'-pyridyl)-3-(3"-cyanophenyl)benzo[e]indole (4),respectively.This reaction proceeds with a high degree of stereo-selectivity with a translds ratio of about 98:2 at elevated temperature.Compounds 1,2,and 4 crystallize in a noncentrosymmetric space group (Pca2_1,,Pca2_1,and Cc),while compound 3 has a chiral space group (P2_1).These successfully acentric packing arrangements are probably due to the molecule bearing both two chiral centers and potential hydrogen-bonding groups.Furthermore,the reaction of racemic 6-hydroxy-2'-methyl-2-naph-thaleneacetic acid with ethyl-2-cyano-l-(4/-pyridyl)acrylic acetate in the presence of piperidine gives l-pyridyl-2-ethoxycarbonyl-3-amino-lH-naphtho-[2,l-b]pyran-2'-methylacetic acid (5),which likewise crystallizes in a chiral space group.All of compounds are second harmonic generation (SHG)active,and have a very strong SHG response approximately about 8.0,5.0,12.0,6.0,and 1.4 (for 1-5 compounds)times that of urea.Ferroelectric property measurements indicate that compounds 1,2,4,and 5 may display ferroelectric behavior.