Synthesis and 2D self-assembly at the liquid-solid interface of end-substituted star-shaped oligophenylenes

We report here on the synthesis and self-assembly of four star-shaped trigonal 1,3,5-tris-(1,1-biphenyl-4-yl)-benzene (TBB) derivatives substituted by different functional groups on the terminal positions of the three arms of the molecule: COOCH3 (1), COOH (2), NH2 (3), and CN (4). Self-assembly of the triester TBB 1 and tricyano TBB 4 compounds is investigated at the liquid/graphite interface using scanning tunneling microscopy (STM). When deposited from 1-phenyloctane as the solvent the triester TBB 1 first forms a chiral open network (Phase I) which does not evolve with time. In turn, when deposited from tetrahydronaphthalene, TBB 1 also forms a chiral open network but with different lattice parameters as compared to Phase I and with solvent molecules co-adsorbed inside the nanopores (Phase II). In tetrahydronaphthalene, the initial nanoporous structure of TBB 1 (Phase II) progressively evolves into a chiral close-packed row-like structure where molecules are associated two-by-two in a head-to-tail fashion to form pairs (Phase III). Finally, when deposited from 1-phenyloctane the tricyano TBB 4 only forms short-range ordering with an open honeycomb structure and a close-packed row-like structure coexisting on the surface.