Abstract

Palladium-catalyzed cross-coupling between 3,4-dialkoxyphenylboronic acids (1a–d) and 2,3,6,7,10,11-hexabromotriphenylene (2) provided 2,3,6,7,10,11-hexakis[3,4-bis(alkoxy)phenyl]triphenylenes, C₁₈H₆[C₆H₃(OC_nH_{2n + 1})₂]₆ where n = 6, 8, 10, and 12 (3a–d). Cyclodehydrogenation of the aryl-substituted triphenylenes 3a–d using ferric chloride oxidation followed by methanol reduction produced 6,6′,6″,7,7′,7″,10,10′,10″,11,11′,11″-dodecaalkoxy-2,3′:3,2″:2′,3″-tris(triphenylenylene)s, C₅₄H₁₈(OC_nH_{2n + 1})₁₂ where n = 6, 8, 10, and 12 (4a–d). The mesomorphic properties of the compounds 3a–d and 4a–d were investigated by differential scanning calorimetry (DSC) measurements, polarizing microscopy, and wide angle X-ray diffraction (WAXD). The triphenylenes 3a–d exhibited a columnar mesophase in the range of 111–126, 85–104, 74–103, and 47–101 °C, respectively. Upon oxidation of the moiety, the columnar mesophases shift to higher temperatures and exist in a much broader range of temperatures: for the tris(triphenylenylene)s 4a–d, they have been observed in the range of 180–430, 150–370, 120–322, and 104–306 °C, respectively. Finally, the self-assembly at the interface between a solution of 4c and a graphite substrate has been studied by scanning tunneling microscopy. Molecularly resolved imaging revealed a highly ordered monolayer exhibiting a two-dimensional hexagonal lattice.