Dibenz[a,c]anthracene derivatives exhibiting columnar mesophases over broad temperature ranges

Abstract

We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges.

Probing the structural features that influence the mesomorphic properties of substituted dibenz[a,c]anthracenes

“…19 We also demonstrated that electrophilic bromination introduced substituents in the 10-and 13-positions. By careful control of the stoichiometry of bromine added, either the monobromo-derivative 6 or the dibromo-derivative 4 could be formed.…”

“…Variable-temperature powder X-ray diffraction studies on a representative compound in this series supports the phase assignment as a columnar hexagonal mesophase. 19 It is noteworthy that most of the compounds in series 4 do not crystallize D r a f t on cooling from the columnar mesophase but instead form glasses that preserve the order of the columnar mesophase. In some cases these glass transitions could be distinguished by DSC, while in other cases they were determined by polarized optical microscopy as the point at which the textures no longer changes upon shearing or compression.…”

“…Specifically, we compared the mesomorphic behaviour of compounds 3-7, which had been previously reported, 11,19 to compounds 8-10, which were prepared in this study.…”

“…The appropriate 2,3-dialkoxy-6,7-dibromonaphthalene 19,25,26 (11a-c) and dialkoxyphenyl boronate ester (12a-c) 19 underwent Suzuki cross-coupling to yield compounds 13a-i (Scheme 1). While the Suzuki couplings gave the desired diaryl naphthalenes in moderate to good yields, purification of these compounds proved challenging: in many cases side-products reaction remained after column chromatography and these relatively low-melting solids were difficult to purify by recrystallization.…”

“…2-7), where the PAH core is extended as compared to the corresponding triphenylenes, have until recently received relatively little attention as potential columnar liquid crystalline materials. 11,[19][20][21] Williams and coworkers were the first to report an example of a dibenzanthracene derivative (3) exhibiting a columnar hexagonal mesophase. 11 The mesophase range of 3 was much broader than that of the corresponding triphenylene, suggesting that extending the aromatic core stabilizes the mesophase through improved π-stacking interactions.…”