Increasing 3D Supramolecular Order by Decreasing Molecular Order. A Comparative Study of Helical Assemblies of Dendronized Nonchlorinated and Tetrachlorinated Perylene Bisimides

A nonplanar, twisted, and flexible tetrachlorinated perylene bisimide (Cl₄PBI) was functionalized with two AB₃ minidendrons containing hydrogenated or semifluorinated dodecyl groups. The hydrogenated dendron was attached to the imide groups of Cl₄PBI via <i>m</i> = 0, 1, and 2 methylenic units, whereas the dendron containing semifluorinated groups was attached via <i>m</i> = 3 or a di­(ethylene oxide) linker (<i>m</i> = 2EO). The supramolecular structures of these compounds, determined by a combination of differential scanning calorimetry, X-ray diffraction, and solid-state NMR, were compared with those of nonchlorinated planar and rigid PBI reported previously, which demonstrated the thermodynamically controlled formation of 2D periodic arrays at high temperatures and 3D arrays at low temperatures. The molecularly less ordered Cl₄PBI containing hydrogenated dendrons self-organize into exclusively 3D crystalline periodic arrays under thermodynamic control for <i>m</i> = 0 and 2, while the more highly molecularly ordered PBI produced less stable and ordered 3D crystals and also 2D assemblies. This induction of a higher degree of 3D order in supramolecular assemblies of the less well-ordered molecular building blocks was unanticipated. The semifluorinated dendronized Cl₄PBI with <i>m</i> = 3 formed a 2D columnar hexagonal array under kinetic control, whereas the compound with <i>m</i> = 2EO formed an unusual 2D honeycomb-like hexagonal phase under thermodynamic control. These Cl₄PBI compounds provide a new route to stable crystalline assemblies via thermodynamic control at lower temperatures than previously obtained with PBI, thus generating 3D order in an accessible range of temperature of interest for structural analysis and for technological applications