Self-assembled molecular architectures on surfaces: New strategies involving metal-organic copolymers

A combination of oligomeric porphyrin copolymers and bidentate Lewis bases has been used to construct 2-dimensional multilayer molecular architectures on siloxane-derivatized glass substrates. The key to this supramolecular c hemistry is coordinate covalent bonding between zinc metalated porphyrins a nd bipyridyl "spacer" ligands, generating layers in an alternating, iterati ve fashion. UV-vis, XPS, AFM, and X-ray diffraction data support the format ion of ordered thin film arrays. The stepwise deposition of each porphyrin layer is tracked by the linear increase in the absorbance of the porphyrin Soret band. XPS results demonstrate that the pyridinium coupling in the fir st monolayer is susceptible to X-ray decomposition during prolonged exposur e. Extremely weak emission in the 600-800 nm region is attributed to the lo w chromophore concentration in the multilayer films. These results contrast sharply with those of spin-coated polymer thin films and represent an enco uraging first step toward the design of new multilayer architectures.