Synthesis, aggregation, and adsorption phenomena of shape-persistent macrocycles with extraannular polyalkyl substituents

The synthesis of shape-persistent macrocycles based on the phenyl-ethynyl b ackbone containing various extraannular alkyl side chains is described. Alt hough compound solubility increases with increasing size of the side groups , decreasing the solvent polarity induces aggregation of the rings by nonsp ecific interactions. This was investigated by proton NMR spectroscopy. The magnitude of aggregation can be varied by using solvent mixtures of differe nt hexane content, supporting the model of a solvophobic effect. From 1,2,4 -trichlorobenzene solution the macrocycle Ic adsorbs at the surface of high ly oriented pyrolitic graphite (HOPG). The two-dimensional order of the str ucture was investigated by scanning tunneling microscopy (STM) revealing th e formation of a two-dimensional lattice of p1(2)mm symmetry with lattice p arameters A = 3.6 nm, B = 5.7 nm, and Gamma = 74 degrees.