π-Extended Pentalenes: The Revival of the Old Compound from New Standpoints

• Published in: Chemical record Vol. 15; no. 6; pp. 1045 - 1059
• Main Authors: Kawase, Takeshi, Nishida, Jun-ichi
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.12.2015
• Subjects: aromaticity; cross-coupling; density functional calculations; fused-ring systems; materials science; cross-coupling; density functional calculations; fused-ring systems; materials science; aromaticity
• ISSN: 1527-8999; 1528-0691
• DOI: 10.1002/tcr.201402093

Polycyclic conjugated systems bearing carbocyclic five‐membered rings have attracted much attention due to their novel electronic properties and utility in organic electronic devices. Despite possessing a 4nπ electron periphery, dibenzopentalenes have a planar structure and are fairly stable. Thus, appropriate modifications should provide desirable electronic properties. Recently, we have discovered novel Ni‐catalyzed coupling reactions that constitute a versatile new route to dibenzopentalene derivatives from readily available o‐bromoethynylbenzenes. Moreover, we developed another dibenzopentalene synthesis using indenone derivatives as important intermediates. These methods are applicable to π‐extended pentalene derivatives possessing various functional groups and aromatic ring systems. Among them, a dinaphthylpentalene derivative shows a high hole mobility (1.8 × 10−3 cm2 V−1 s−1) for an amorphous material. Furthermore, this is the first pentalene derivative that can be employed as a p‐type material for organic heterojunction photovoltaic cells (PCE = 0.94%, VOC = 0.96 V) and as organic thin‐film semiconductors. Polycyclic conjugated systems bearing carbocyclic five‐membered rings have attracted much attention due to their novel electronic properties and utility in organic electronic devices. Two novel synthetic routes to dibenzopentalene derivatives are described, which are applicable to π‐extended pentalene derivatives possessing various functional groups and aromatic ring systems. In particular, a dinaphthylpentalene derivative was obtained that shows a high hole mobility for an amorphous material and could be employed in organic heterojunction photovoltaic cells and organic thin‐film semiconductors.