Solution Versus On‐Surface Synthesis of Peripherally Oxygen‐Annulated Porphyrins through C−O Bond Formation

Abstract

This study investigates the synthesis of tetra‐ and octa‐O‐fused porphyrinoids employing an oxidative O‐annulation approach through C−H activation. Despite encountering challenges such as overoxidation and instability in conventional solution protocols, successful synthesis was achieved on Au(111) surfaces under ultra‐high vacuum (UHV) conditions. X‐ray photoelectron spectroscopy, scanning tunneling microscopy, and non‐contact atomic force microscopy elucidated the preferential formation of pyran moieties via C−O bond formation and subsequent self‐assembly driven by C−H⋅⋅⋅O interactions. Furthermore, the O‐annulation process was found to reduce the HOMO–LUMO gap by lifting the HOMO energy level, with the effect rising upon increasing the number of embedded O‐atoms.