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We have used pressure-area isotherms, X-ray diffraction, atomic force microscopy, and infrared dichroism to study Langmuir and Langmuir-Blodgett films of 2,3,6,7,10,11-hexaalkoxytriphenylenes which were selectively di-and trifunctionalized with C n H 2n -OH groups at the 2,3-, 2,6-, 3,6-, and 3,6,10-positions. The bulk phase behavior of these compounds was also established with use of polarizing microscopy and differential scanning calorimetry. At the air-water interface, the hydroxy groups make contact with the water, and the Langmuir film stability is strongly correlated with proximity of the hydroxy groups on the molecule. Mixtures of 2,3-and 3,6-isomers display a dramatic increase of the liquid-crystalline mesophase temperature range compared to the pure compounds. The mixtures also have lower molecular areas at the air-water interface and produce thin films with a complex superlattice structure of disk tilts, showing for the first time the ability of triphenylene isomer alloys to self-organize.

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We have used grazing incidence X-ray diffraction and X-ray specular reflectivity to study the behavior of platelike hexaalkoxytriphenylene derivatives at the air−water interface. The data are consistent with a two-dimensional columnar mesophase, wherein the molecules are arranged “edge-on” to the water surface, with intercolumnar spacings of 13−19 Å. We propose a molecular conformation in which hydrophobic tails lie parallel to the water surface so as to allow the hydrophilic oxygen atoms to directly contact the water surface. In equimolar mixtures of two disubstituted amphiphilic isomers of a triphenylene derivative, we see direct evidence for structural self-organization and intercolumnar order. We also present indirect evidence for orientational self-organization in symmetrically substituted triphenylene derivatives.

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