The effect of terminal dimethyl and diethyl substituents on the J-aggregate-like molecular arrangement of bisazomethine dye molecules

Abstract

Derivatives of 2,3-bis[(E)-4-(diethylamino)-2-alkoxybenzylideneamino]fumaronitrile (DEA) form J-aggregate-like 2-dimensional (2-D) arrangements of π–π-stacked molecules in the solid state. The structural features of the 2-D molecular arrangements were controlled by the alkoxy substituents of the DEA derivatives. In this study, the single crystal structures of six 2,3-bis[(E)-4-(dimethylamino)-2-alkoxybenzylideneamino]fumaronitrile (DMA) derivatives are reported, five of which formed J-aggregate-like 2-D molecular arrangements in the solid state. The molecular arrangements of four of the six DMA derivatives were geometrically compared with those of the corresponding four DEA derivatives, to evaluate the effect of the terminal dimethyl and diethyl substituents on the J-aggregate-like 2-D molecular arrangement. Lattice energy calculations were also carried out to interpret the effects of the terminal dialkyl substituents on the crystal structures from an energetic perspective. The dialkyl substituents of the selected DMA and DEA derivatives did not influence the formation of 1-D π–π stacking motifs. However, the location of the terminal dialkyl substituents influenced the spacing between molecules aligned along the long axis and this was found to be key in determining the formation of J-aggregate-like 2-D arrangements.