Desymmetrization of 3,3'-bis(acylamino)-2,2'-bipyridine based discotics: the high fidelity of the self-assembly behavior in the liquid crystalline state and in solution

Two novel nonsymmetrical disc-shaped molecules 1 and 2 based on 3,3-bis(acylamino)-2,2-bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self-assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Two columnar rectangular mesophases (Colr) have been identified, whereas for C3-symmetrical derivatives only one Colr mesophase has been found.[1] In solution, the molecularly dissolved state in chloroform was studied with 1H NMR spectroscopy, whereas the self-assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C3-symmetrical derivatives, a mixing experiment of chiral 1 with C3-symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self-assembly. This helical J-type self-assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2, functionalized with a hydrogen-bonding acceptor moiety, might perform secondary interactions with molecules such as acids.