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摘要
Bithiophenyl-based diaminotriazine derivatives(2TDT-n,n= 10, 12, 16, and 18) with different chain lengthsdisplay colhex/p6mmmesophases. Their supramolecular self-assembled mechanism is investigated using scanning tunnelingmicroscopy (STM) at the 1-octanoic acid/graphite interface atvarious concentrations. The chain length effect on the two-dimensional adlayers is observed in this system, and 2TDT-nmolecules show a structural phase transition from the four-leafarrangement to the two-row linear nanostructure accompanied bythe emergence of molecular isomerization with the increase of theside-chain length. The self-assembled structure of 2TDT-10 iscomposed of a four-leaf pattern with uniform s-cisconformers. In2TDT-12, three kinds of nanostructures (bamboo-like, two-rowlinear pattern-I, andflower-like) are observed. These nanostructures are randomly constituted bycisandtransconformers, and theratios of the s-cisconformer in three kinds of patterns are 55.7, 42.3, and 62.5%, respectively. Furthermore, whenn= 16 and 18, theratio of the s-cisconformer further decreases to 19.0 and 4.3%, respectively. Those molecules mainly form linear nanostructuresconsisting of s-transconformers. Therefore, it is reasonable to conclude that the side-chain length has a great effect on the self-assembled patterns and the molecular conformation of bithiophenyl-based diaminotriazine derivatives. Density functional theorycalculations are applied to optimize molecular conformers and assess their single-point energies, showing that the s-cisconformationhas higher energy than the s-transconformer. We speculate that the ratio of two conformers in nanostructures might be similar tothat of the liquid crystalline phase.
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单位云南大学
