Optical second harmonic generation in achiral bis(n-alkylamino)dicyanoquinodimethanes: Alkyl chain length as the design element

Chain length of substituted n-alkyl groups is proposed to be a convenient d esign element for the generation of noncentrosymmetric crystal lattices of interest in optical second harmonic generation (SHG). Powder studies on 7,7 -Bis(m-alkyl amino)-8,8-dicyanoquinodimethanes indicate that moderate solid -state optical SHG is obtained when the alkyl chains are of length 4, 5, an d 6, and no detectable SHG occurs when the chains are of length 0, 3, 7, 8, and 12, The significant role of the intermediate alkyl chain length in gen erating noncentric crystal lattices is examined using the crystal structure s of the propyl, butyl, and octyl derivatives presented in this paper.