Combined In-Solution and On-Surface Synthesis of a Fully Fused Cross-shaped Phthalocyanine Pentamer

Phthalocyanines (Pcs) are a class of technologically relevant tetrapyrrolic macrocycles that offer rich photophysical properties as well as excellent tunability by means of chemical functionalization. Among such functionalization strategies, the synthesis of multinuclear, fully fused Pcs – adjacent macrocycles seamlessly fused through a shared aromatic ring into a continuous π-system – is particularly appealing for the preparation of new, exotic, atomically precise carbon frameworks. However, the notoriously low solubility of Pcs typically impedes the synthesis of oligomers beyond trimers. In addition, the positional control for specific units in large low-symmetry frameworks is particularly challenging. In this work, taking advantage of the benefits of on-surface synthesis under ultra-high vacuum (UHV) conditions, we present a strategy that allows the on-surface synthesis of cross-shaped Pc pentamers. This pentamer, which bears two different metal ions with pre-defined positional control, shows a small transport gap of 1.15 eV on Au(111).