Core-shell nanoparticles composed of an iron oxide core encapsulated with an ogranic shell of porphyrins were synthesized using a “one-pot” method. Multilayers of porphyrins were covalently linked to the metal nanoparticles with metal-O-Si- bridges. Porphyrins are macrocyclic compounds which have a rigid aromatic structure, are thermally stable, and have useful optical and electronic properties that have potential for molecular electronics. Encapsulating nanoparticles with porphyrins in a core-shell design can impart multiple functionalities for applications with tunable optical and electronic properties. A protocol using silicon tetrachloride was used to form a skewered arrangement of co-planar porphyrins to form an organic shell of porphyrins surrounding the outer periphery of metal nanoparticles (e.g. gold, iron oxide). The porphyrin shell is formed by linking free-base porphyrins with Si-O-Si bridges in a shish-kebob arrangement with a silicon atom coordinated to the center of the macrocycles. The porphyrin shell is covalently anchored to the core metal nanoparticle through silane coupling and the skewered porphyrin stacks adapt a coplanar configuration relative to the surface. The thickness of the shells can be tuned by synthetic parameters such as concentration and immersion intervals. Samples were characterized with tapping-mode AFM to directly compare the sizes and shapes of nanoparticles before and after encapsulation with porphyrins. The differences in surface morphology between the soft organic shell and hard inner metal cores were sensitively distinguished with AFM phase images. The synthetic approach should be generic for encapsulating metal nanoparticles with organic shells of macrocyclic porphyrinoid molecules.

Core-shell morphology of metal nanoparticles encapsulated with silane-coupled porphyrins characterized using scanning probe microscopy

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