On-surface polyarylene synthesis by cycloaromatization of isopropyl substituents

Immobilization of organic molecules on metal surfaces and their coupling via thermally induced C–C bond formation is an important technique in organic and polymer synthesis. Using this approach, insoluble and reactive carbon nanostructures can be synthesized and the reactions monitored in situ using scanning probe microscopy methods. The diversity of conceivable products, however, is limited by the number and variety of known on-surface reactions. Here, we introduce the on-surface synthesis of polyarylenes by intermolecular oxidative coupling of isopropyl substituents of arenes. This [3+3] dimerization reaction forms a new phenylene ring and can be regarded as a formal cycloaromatization. The synthetic value of this reaction is proved by the synthesis of polyarylenes and co-polyarylenes, which we demonstrate by synthesizing poly(2,7-pyrenylene-1,4-phenylene). Scanning tunnelling microscopy and non-contact atomic force microscopy studies, complemented by density functional theory calculations, offer mechanistic insight into the on-surface cycloaromatization reaction.