Synthesis of unsymmetrical dibenzoquinoxaline discotic mesogensElectronic supplementary information (ESI) available: full synthetic and analytical details, POM images. See http://www.rsc.org/suppdata/cc/b4/b400998c/

Abstract

Unsymmetrical dibenzophenazine discotic mesogens were prepared via the corresponding tetraalkoxybenzil derivatives. These dibenzophenazines exhibit Colho phases over extremely broad temperature ranges.

Modular assembly of elliptical mesogens

“…Compounds P6 and P10 both exhibit an ordered hexagonal columnar phase (Col ho ) and crystallize upon cooling, which is typical for molecules of this type that form no hydrogen bond on their own [5,6]. Both the melting and clearing temperatures of P6 were found to be higher than those of P10, and P6 is liquid crystalline over a broader temperature range.…”

“…The versatile approach previously developed for the synthesis of discotic liquid crystals by the coupling of a 2,3,6,7-tetraalkoxyphenanthrene-9,10-dione with 1,2-diamines such as 2a, 2b or 2c [5,6,14] provides a simple route to discotic mesogens containing a pyridine ring (P6, P10, SP6, SP10), as illustrated in scheme 1.…”

“…One major difference that was observed, however, was the lower melting and clearing temperatures of the mixtures compared with the pure acids. This depression of the phase transition temperatures may reflect the lower symmetry of the mixed complexes relative to the acid dimers, since less symmetrical structures generally undergo order-disorder transitions at lower temperatures [6].…”

“…While employing acid dimers is useful for creating such structures, it unfortunately imposes the restriction that only symmetrical systems can be studied. Since both symmetry and shape are expected to have a profound impact on phase behaviour [6], we were interested in exploring a more versatile approach that would permit the construction of ellipses from two different disc-shaped components. The strong tendency of carboxylic acids to hydrogen bond with pyridine derivatives has been used to assemble rod-like mesogens [7,8], and therefore suggested itself as a convenient method for the creation of elliptical structures.…”

Side-chain shuffling: regioselective synthesis of mixed tail discotic mesogens

“…Moreover, quinones such as 9 and tolanes such as 7 are potential precursors to a range of mesogens, including triphenylenes, 15-17 dibenzoquinoxalines, 13,18,19 dibenzophenazines, 3,20-27,27-29 phthalocyanines 18,30 and metallomesogens. Although the current work has focused on a series of isomers containing just two pairs of side chains, it is worth noting that mesogens with any combination of alkoxy groups can be regioselectively prepared in this manner.…”