On-Surface Crystallization Behaviors of H-Bond Donor-Acceptor Complexes at Liquid/Solid Interfaces

Two-dimensional (2D) crystallization behaviors of A-TPCn (n = 4, 6, 10), T3C(4), and hydrogen-bonded complexes T3C(4)@TPCn (n = 4, 6, 10) are investigated by means of scanning tunneling microscope (STM) observations and density functional theory (DFT) calculations. The STM observations reveal that A-TPC4, A-TPC10, and T3C(4) self-organize into dumbbell-shaped structures, well-ordered bright arrays, and zigzag structures, respectively. Interestingly, T3C(4)@TPC10 fails to form the cage-ball structure, whereas T3C(4)@TPC4 and T3C(4)@TPC6 co-assemble into cage-ball structures with the same lattice parameters. The filling rates of the balls of these two kinds of cage-ball structures depend heavily on the deposition sequence. As a result, the filling rates of the cages in T3C(4)/A-TPCn (n = 4, 6) with deposition of T3C(4) anterior to A-TPC are higher than those in A-TPCn/T3C(4) (n = 4, 6) with the opposite deposition sequence. Furthermore, lattice defects formed by T3C(4) coexist with the cage-ball structures. Moreover, the similar energy per unit area of lattice defects (-0.101 kcal mol(-1) angstrom(-2)) and the two cage-ball networks (-0.194 and -0.208 kcal mol(-1) angstrom(-2), respectively), illustrating the similar stabilities of lattice defects and cage-ball networks, demonstrates the rationality of lattice defects. Combining STM investigations and DFT calculations, this work could provide a useful approach to investigate the 2D crystallization mechanisms of supramolecular liquid crystals on surfaces.