Extended triphenylenes: synthesis, mesomorphic properties and molecularly resolved scanning tunneling microscopy images of hexakis(dialkoxyphenyl)triphenylenes and dodeca(alkoxy)tris(triphenylenylene)s

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-h exakis[3,4-bis(alkoxy)phenyl]triphenylenes, C18H6[C6H3(OCnH2n + 1)(2)](6) w here n = 6, 8, 10, and 12 (3a-d). Cyclodehydrogenation of the aryl-substitu ted 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(OCnH2n + 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) measu rements, polarizing microscopy, and wide angle X-ray diffraction (WAXD). Th e triphenylenes 3a-d exhibited a columnar mesophase in the range of 111-126 , 85-104, 74-103, and 47-101 degrees 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 degrees C, respectively. Finally, the self-assembly at the interface b etween a solution of 4c and a graphite substrate has been studied by scanni ng tunneling microscopy. Molecularly resolved imaging revealed a highly ord ered monolayer exhibiting a two-dimensional hexagonal lattice.