Real-space imaging and manipulation of chemical reactions at solid-liquid interfaces

Insight into mechanisms of chemical reactions catalyzed by organic molecules is one of the fundaments of natural science. Information about these mechanisms can be obtained by a scala of conventional spectroscopic techniques; however, the advent of scanning probe microscopies has opened new approaches to study chemical reactions at surfaces. In particular Scanning Tunneling Microscopy (STM) offers the possibility to obtain information down to the submolecular level. The majority of such studies is limited to ultra-high vacuum (UHV) conditions, which, however, are not realistic situations in the case of larger scale chemical laboratories or biological systems. In this proposal, such unrealistic situations are turned around, and all stages of a chemical reaction will be studied and manipulated at solid-liquid interfaces in realistic environments. Catalytic surfaces consisting of monolayers of self-assembled metallo-porphyrins, catalysts which will be synthesized using standard organic chemistry procedures, will be investigated down to the submolecular level with the help of STM. Subsequently, the surfaces will be studied in real-space and real-time with STM during a chemical reaction, examining the geometrical and electronic properties of the catalysts at the single molecule level. Initially, the emphasis will be on oxidation catalysis at solid-liquid interfaces, using manganese(III)porphyrin catalysts, and it is the aim to image all the molecular species present during the reaction, i.e. the catalyst, reactants, reaction products, and mostly desired the transition state, in which a reactant is connected to the catalyst. Particular attention will be directed to the visualization and characterization of the catalytic metal centers of the porphyrins. Attempts will be undertaken to effect changes in their oxidation state with the STM tip, and thus turn the chemical reaction on or off. To further develop the reactor-STM, STMs will be equipped with liquid cells and controlled atmosphere chambers, allowing the possibility to carefully administer additives and gases. Keywords: scanning tunneling microscopy, solid-liquid interfaces, catalysis, porphyrins