As. Shetty et al., ASSEMBLY OF AMPHIPHILIC PHENYLACETYLENE MACROCYCLES AT THE AIR-WATER-INTERFACE AND ON SOLID-SURFACES, Journal of the American Chemical Society, 118(39), 1996, pp. 9409-9414
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.