Assemblies of “Hinged” Iron−Porphyrins as Potential Oxygen Sensors

Sequential self-assembly of a two-component system on a solid support is described with respect to structure and function. Two ligands, which bind to the semiconductor surface through one end and axially ligate a heme analogue at the other end, are described. Monolayer assemblies of complexes formed by these ligands and iron-porphyrin perform reversible binding of molecular oxygen. In the monolayer, a metalloporphyrin (the sensing unit) is held by the intervening ligand that serves as a “hinge”, away from the solid surface. Sensing events based on porphyrin chemistry are communicated via the ligand to the solid support. The transduction manifests itself as a change in the solid's surface electronic properties. Synthesis of the ligands and analysis of its complex formation with FeIII-porphyrin are described. The anisotropic orientation of the porphyrin ring within the ligand cavity, due to restricted rotation around the FeIII−N imidazole bonds, was probed by 1H NMR measurements in solution. We show that th...