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

Abstract

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. Scheme 1 Chemical structures of dyes 1-8.

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

“…Within the 2-D layers that are formed, the molecules are stacked with two different types of small slip angles along the long molecular axes. 30,35 As shown in Figure 1(b), the stacked molecules form a staircase-like arrangement in the 2-D layers. The 2-D molecular arrangements of the DEA derivatives are similar to the proposed 2-D molecular arrangements of J-aggregates.…”

“…28 Crystal structures of the dye molecules show that they form J-aggregate-like two-dimensional (2-D) stacked layers. 30,35 The features of the crystal structures of the nine reported DEA derivatives are schematically summarised in Figure 1. Within the 2-D layers that are formed, the molecules are stacked with two different types of small slip angles along the long molecular axes.…”

“…The alkoxy groups are parallel to the molecular π-planes. However, the larger decyloxyl substituents project out of the π-plane; this leads to a dislocation of the π-π stacking in the short molecular axis, and consequently small interlayer separations (Figure 1(d)) 30 The 3-D crystal structures of the DEA derivatives are clearly partitioned into two parts. One part corresponds to the 2-D π-π stacking molecular layer.…”

“…A dislocation of the π-π stacked molecules along the short molecular axes was found in the 2-D layers of 1b-1f, this is similar to that of the DEA derivatives with decyloxy substituents. 30 In order to systematically evaluate the effects of the terminal dimethyl and diethyl substituents on the J-aggregate-like 2-D molecular arrangements, the four crystal structures of 1c-1f were geometrically compared to the four reported crystal structures of the corresponding DEA derivatives, 2c-2f. The lattice energies were also calculated for 1c-1f and 2c-2f to interpret the substitution effects from an energetic perspective.…”

J-aggregate structure in a chloroform solvate of a 2,3-dicyanopyrazine dye ? Separation of two-dimensional stacking dye layers by solvate formation

“…It is also very important that these bulk J-aggregates can be prepared through a conventional method. To achieve these demands, J-aggregate formation in a stable crystalline state [13] is a promising solution even though there is currently no design strategy for obtaining J-aggregate crystals. Here, we report the crystal structure and solid state optical properties of a chloroform solvate of a 2,3-dicyanopyrazine dye as an example of a potential crystal structure towards the design of J-aggregate crystals.…”