Geometry and bond-length alternation in nonlinear optical materials. III. Structural parameters of two chromophores containing aromatizable donorsPart II: Gainsford, Bhuiyan & Kay (2008a).

The planar component of 2-{3-cyano-4-[3-(1-decyl-1,4-dihydroquinolin-4-ylidene)prop-1-enyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}malononitrile, C(32)H(46)N(4)O, (I), forms into layers parallel to the (\overline{1}01) plane. The larger of the two spaces between layers is filled by the alkyl chains, giving a ;sandwich stack' appearance. The packing of 2-{3-cyano-4-[5-(1-decyl-1,4-dihydroquinolin-4-ylidene)penta-1,3-dienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}malononitrile, C(34)H(38)N(4)O, (II), which has partial disorder in the 1-decyl group, utilizes weak C-H...N, C-H...O and C-N...pi interactions in a three-dimensional ;herring-bone' array with molecular segments parallel to the (111) and (\overline{1}1\overline{1}) planes. Different rotational isomers with respect to the polyene chain and the 5,5-dimethyl-2,5-dihydrofuran-2-ylidene link are observed in the two structures. The significance of the study lies in the delocalization of charge along the polyene chain and the supramolecular aggregation present, which highlight the difficulty in obtaining the noncentrosymmetric alignment required for high nonlinear optical (NLO) responses in zwitterionic chromophores.