Many chemical reactions are catalyzed by metal complexes, and insight in their reaction mechanisms is of fundamental importance for the design of new chemical processes. A wealth of conventional spectroscopic techniques is available to study reaction mechanisms at the ensemble level, but the emergence of scanning probe microscopy has enabled the possibility to obtain information about reactivity at subnanometer scale. I will discuss single molecule studies of the behavior of reactive molecules in an environmentally controlled Scanning Tunneling Microscope (STM). Reactions of manganese(III) porphyrins (Fig. 1A), self-assembled at a solid/liquid interface, with oxygen are investigated in real-space and real-time. Upon exposing these porphyrins to an atmosphere of O2or to a single oxygen donor, STM revealed a variety of reactions which are detected by clear changes in porphyrin signature in the STM images (Fig. 1B). The signatures can be assigned to the starting compound, reaction products, and intermediates, and their dynamical interchange can be monitored for hours. Furthermore, the reactivity of the porphyrins can be controlled by the applied bias voltage. These studies revealed unique mechanistic insights at the single molecule level that remain hidden in ensemble measurements. Figure 1   (A) Structure of the Mn(III) porphyrin. (B) STM image (13 � 7 nm2) of 4 different signatures of the Mn porphyrin at a graphite/liquid interface under an oxygen atmosphere.

Revealing and manipulating single molecule reactivity in an environmentally controlled liquid-STM

247th National Meeting (2014)

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