Complex ordering in thin films of di- and trifunctionalized hexaalkoxytriphenylene derivatives

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 CnH2n-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.