Organometallic Photochemistry: Basic Principles and Applications to Materials Chemistry

An overview is presented of organometallic photochemistry and its applications to materials chemistry. The excited states of typical organometallic complexes include ligand field excited states, metal-to-ligand charge-transfer excited states, ligand-to-metal charge-transfer excited states, Rydberg excited states, and excited states associated with metal-metal bonds. In general, each of these excited states leads to a particular type of photochemical reaction. Ligand field excited states typically lead to metal-ligand bond heterolysis, charge-transfer states to redox processes, and Rydberg states to homolytic metal-ligand bond dissociation. Excitations involving metal-metal bond states lead to metal-metal bond homolysis. Each of these photoprocesses has uses in materials chemistry. Metal-ligand bond dissociations are used to deposit thin films of metals or alloys. The thin films thus produced are used in the manufacture of semiconductors or microcircuitry. Likewise, metal-ligand bond dissociations are used to generate multiply coordinatively unsaturated catalysts for epoxide polymerization. Homolytic dissociations of metal-ligand bonds are used to initiate radical chain polymerization reactions. Irradiation of organometallic compounds on surfaces can be used to derivatize the metal surface. In these processes, a metal-ligand bond is dissociated and then replaced by a functionalized ligand bearing a redox active metal center. These derivatized surfaces are potentially useful in the fabrication of microfabricated circuits.