Constructing Bilayer-type Layered Herringbone Packing in Dithienoa,hanthracenes for Solution-processable Organic Semiconductors

The bilayer-type layered herringbone (LHB) packing has enhanced layered crystallinity, which is favorable for achieving efficient carrier transport. By utilizing asymmetric phenyl-alkyl substitution, this study successfully established a bilayer-type LHB packing for angular dithienoa,hanthracene (aADT), which itself does not have a layered structure. Their packing motifs are highly associated with the alkyl chain length. Ph-aADT-C10 and Ph-aADT-C12 formed similar bilayer-type LHB packing motifs, while Ph-aADT-C8 with short octyl chain exhibited a different arrangement where the π-cores and octyl chains are interdigitated with each other, revealing short alkyl chains impede the LHB packing. Furthermore, the packing structure clearly affected the film-forming ability: Ph-aADT-C10 and Ph-aADT-C12 produced relatively uniform crystalline thin films, while Ph-aADT-C8 afforded only thick and discontinuous crystalline domains. Notably, characteristic p-channel transistor characteristics with high mobility up to 1.46 cm2/(V s) were found in Ph-aADT-C12. Our findings reveal that asymmetric phenyl-alkyl substitution can serve as an effective method that can be utilized on various π-cores for exploring their carrier-transport potential by constructing a bilayer-type LHB structure.