Metalloporphenes: Synthesis and Characterization

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With support from the Chemical Structure, Dynamics & Mechanisms-B (CSDM-B) Program of the Chemistry Division, Professor Josef Michl of the Department of Chemistry at the University of Colorado at Boulder is developing a new family of ultra-thin polymers that are designed to be one-atom thick and to possess interesting optoelectronic properties. The goal of this research is to explore the characteristics of these metal ion containing polymers and to exploit them for the development of optoelectronic devices, such as transistors for nanoelectronics. The project lies at the interface of organic, inorganic, and materials chemistry, and is therefore well suited to the education of scientists at all levels. This group is also well-positioned to provide the highest level of education and training for students underrepresented in science. Outreach activities involving K-12 students will also be part of the project.The new polymers, called metalloporphenes, consist of porphyrin macrocycles fused on all four sides into a planar square array similarly as benzene rings are fused into graphene. The centers of the macrocycles may contain two protons (“free base porphene”) or a divalent metal cation (“metalloporphene”), and the metal atom may carry two, one, or no axial ligands, such that a vast number of finely tunable derivatives are possible. Free-base porphene has been synthesized by oxidative polymerization of a bilayer of zinc porphyrin on the surface of water in a Langmuir-Blodgett trough under controlled surface pressure, using an oxidant contained in the aqueous subphase. The current focus of the project is the unravelling of the kinetics and the mechanism of the formation of a regular polymer, whose single crystalline domains have a coherence length of at least 120 nm, from the preorganized bilayer of monomers, with a simultaneous loss of the zinc cations. A series of techniques will be used to monitor the kinetics of the gradual disappearance of the characteristic spectral signatures of the starting zinc porphyrin, such as its UV-visible (Soret band) and CH stretching absorption and its XPS signals, as a function of surface tension, oxidant nature and concentration, solution pH, substrate deuteriation, etc. It is expected that an understanding of the mechanism of porphene formation will contribute to the development of procedures that will yield larger patches of metalloporphenes containing larger single crystalline domains with fewer defects. These may then be amenable to use as a canvas on which lithographic patterns and possibly even circuitry can be drawn, containing different metal ions and thus different properties in different regions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.