Aromatic Donor-Acceptor Interactions

Aromatic donor-acceptor interactions have proven to be remarkably versatile for the construction of complex molecular systems that fold and assemble in aqueous solution.  Folding molecules of various topologies, duplex formation and even novel DNA binding molecules have been created based on the alternating stacking motif of properly chosen electron rich and electron deficient aromatic units.  More recently, we have used aromatic donor-acceptor interactions to assemble columnar mesophases with tunable properties.  In particular, derivatives of relatively electron rich 1,5-dialkoxynaphthalene (DAN) donors and relatively electron deficient 1,4,5,8-naphthalenetetracarboxylic diimide (NDI) acceptors have been used to direct assembly of extended columns with alternating face-centered stacked structures in the solid state.  A variety of 1:1 DAN:NDI mixtures produced mesophases that were found to be stable over temperature ranges extending up to 110ūC.  Analysis of these mesophases indicates mixtures with soft/plastic crystal phases and a few mixtures with the thermodynamic properties of true liquid crystals, all composed of alternating donor-acceptor columns.  Importantly, a correspondence was found between the clearing and crystallization points of the mesophase mixtures and the melting/clearing points of the component NDI and DAN units, respectively.  This correspondence enables the predictable tuning of mesophase phase transition temperatures.  Classes of derivatives were discovered that exhibited a dramatic and sudden color change (deep red to yellow) upon crystallization of the mesophase due to a phase separation of the component donor and acceptor units.