Electron and proton transfer assemblies and new porous materials from nanometer-scale building blocks

Elegant examples of molecular engineering are found in nature that make our current small devices seem primitive. By using naturally occurring examples we can better imagine how to construct useful three dimensional nanoscaled devices. Electron and proton transfer composites were prepared using a multilayer film growth technique, in which single anionic sheets derived from inorganic solids are interleaved with cationic polyelectrolytes. This method allows for the growth of concentric monolayers of redox-active polymers on high-surface-area silica supports, and for vectorial electron transfer reactions through the layers of the “onion.” Photoinduced charge separation has been observed in composites consisting of an inner polycationic layer of poly(styrene- co-N -vinylbenzyl-N′-methyl-4,4 ′-bipyridine), and an outer polycationic layer of poly[Ru(bpy) ₂(vbpy)]2+, vbpy = 4-vinyl-4′-methyl- 2,2′-bipyridine, bpy = 2,2′ -bipyridine, which are separated by a thin inorganic sheet of Zr(HOPO ₃)₂·H2O. Following the logic of the proton transport mechanism found in biological membranes, a photosensitive proton pump was constructed using the same electrostatic adsorption technique. This composite was prepared with a polymeric form of a luminescent ruthenium complex, poly[Ru(bpy) ₂(bpm)]2+, bpy = 2,2′-bipyridine bpm = 2,2′-bipyrimidine. The pH of a solution in which the composites were suspended changed reversibly when irradiated with visible light. A series of microporous polymer replicas were synthesized using inorganic templates. Zeolites were used as templates to prepare microporous polymer replicas with nanometer sized pore networks. Phenol-formaldehyde polymers were synthesized and cured within the channel networks of zeolites Y, β, and L. Dissolution of the aluminosilicate framework in aqueous IHF yields an organic replica. The zeolite template exerts important topological effects on the structure and physical properties of the replica. A similar process is described for synthesizing mesoscale polymer fibers and mesostructured particles using the well-defined channels of mesoporous silica as a mold. Ordered mesoporous polymers were prepared by replication of colloidal crystals made from 35 nanometer diameter silica spheres. The voids were filled with divinylbenzene (DVB), ethyleneglycol dimethacrylate (EDMA), or a mixture of the two. Polymerization and subsequent dissolution of the silica template leaves a polycrystalline network of interconnected pores. The pore size of the replica polymer depends on the ratio of monomers used in the synthesis.