Effects of alkoxy substitution on the crystal structure of 2,3-bis[(E)-4-(diethylamino)-2-alkoxybenzylideneamino]fumaronitrile derivatives

The bisazomethine dyes derived from diaminomaleonitrile and aminobenzaldehydes, 2,3-bis[(E)-4-(dialkylamino)benzylideneamino]fumaronitrile derivatives, are known to have potential as dyes for forming J-aggregate vapour-deposited films, even though appropriate conditions for preparation of their pure J-aggregate films are unknown. In this study, an attempt was made to investigate the effects of alkoxy substitution on the crystal structures of eight bisazomethine dyes; our final goal was to obtain pure J-aggregates of bisazomethine dyes in a crystalline state. The focus of this study is on the relationship between changes in the molecular structure and the crystal structure, characterized by a two-dimensional molecular stacking layer and its alignment. We found that the interlayer distance between adjacent two-dimensional stacking layers can be controlled by alkoxy substitution, when the substituent chain length is less than C10, without any significant structural changes in the stacking layer. Our observation was confirmed by lattice energy calculations from an energetic perspective. © The Royal Society of Chemistry 2011.