Ring-expansion approach towards extended asymmetric benzopentafulvalenes: overcrowded olefinic structure and chain length-dependent properties

Creating pi-extended benzopentafulvalenes can aid development of novel functional materials for organic electronics. Herein, we describe a facile ring-expansion strategy to allow precise construction of benzopentafulvalenes in an asymmetric benzoannulation mode, which provides an unprecedented opportunity to extend overcrowded olefins. This ring-expansion experienced sequenced skeletal rearrangementviaa crucial spirobicyclic cation intermediate, rationalized by experiments and theoretical calculations. The resulting pi-extended benzopentafulvalenes showed chain length-dependent physical properties. Substituent tuning led to available pi-systems exhibiting LUMO energies comparable with those of fullerenes and stable ionic radicals upon one-electron oxidation/reduction. The pi-extended nonplanar molecules displayed promising air-stable ambipolar semiconducting properties with balanced carrier-transport performances in thin film-fabricated OFETs. Our study provides insights into the fundamental relationships between molecular structures and optoelectronic properties for a new class of asymmetric benzopentafulvalenes.