Surface-Mediated Ring-Opening and Porphyrin Deconstruction via Conformational Distortion
Felix Bischoff, Alexander Riss, Georg S. Michelitsch, Jacob Ducke, Johannes V. Barth, Karsten Reuter, Willi Auwärter
Abstract
The breakdown of macrocyclic compounds is of utmost importance in manifold biological and chemical processes, usually proceeding via oxygenation-induced ring-opening reactions. Here, we introduce a surface chemical route to selectively break a prototypical porphyrin species, cleaving off one pyrrole unit and affording a tripyrrin derivative. This pathway, operational in an ultrahigh vacuum environment at moderate temperature is enabled by a distinct molecular conformation achieved via the specific interaction between the porphyrin and its copper support. We provide an atomic-level characterization of the surface-anchored tripyrrin, its reaction intermediates, and byproducts by bond-resolved atomic force microscopy, unequivocally identifying the molecular skeletons. The ring-opening is rationalized by the distortion reducing the macrocycle's stability. Our findings open a route to steer ring-opening reactions by conformational design and to study intriguing tetrapyrrole catabolite analogues on surfaces.