ASSEMBLY OF AMPHIPHILIC PHENYLACETYLENE MACROCYCLES AT THE AIR-WATER-INTERFACE AND ON SOLID-SURFACES

The assembly of amphiphilic phenylacetylene macrocycles (PAMs), with m olecular structures that vary in terms of the nature and orientation o f their pendant functional groups, has been studied on a Langmuir-Blod gett trough and after transfer onto solid substrates. These monolayer films are of interest as two-dimensional host matrices and shape selec tive membranes whose two-dimensional organization should bring togethe r shape selective compartments. The disk-like PAMs can, in principle, adopt orientations in which the plane of the macrocycle can range from perpendicular (edge-on) to parallel (face-on) at the interface. PAMs functionalized with six hydrophilic groups around the periphery do not prefer the face-on orientation and are most likely tilted, perhaps in a poorly organized state. PAMs that have spatially segregated hydroph ilic and hydrophobic groups adopt the edge-on orientation when the hyd rophilic moieties are carboxylate groups. In contrast, PAMs appended w ith acid moieties do not lead to stable monolayers, most likely becaus e they engage in strong intermolecular hydrogen bonding interactions a s evidenced by H-1 NMR and vapor pressure osmometry of the solutions. Monolayers of the dicarboxylate PAMs were transferred onto fused silic a and Si(100) surfaces and these were in turn characterized by contact angle, ellipsometry, absorption FTIR, and angle-resolved X-ray photoe lectron spectroscopies. Taken together these characterization experime nts strongly support the hypothesis that the dicarboxylate PAMs form a well-ordered and stable two-dimensional array and that they adopt the edge-on configuration with near-vertical orientation of the macrocycl e plane.