Isomers of B←N-Fused Dibenzo-azaacenes: How B←N Affects Opto-electronic Properties and Device Behaviors?

The B <- N unit has a large dipole and it is isoelectronic to C-C moiety with no dipole. Incorporating B <- N units into pi-conjugated system is a powerful strategy to design organic small molecules and polymers with intriguing opto-electronic properties and excellent opto-electronic device performance. However, it is unclear how the B <- N unit affects electronic structures and opto-electronic properties of large pi-conjugated molecules. In this work, to address this question, we developed three dibenzo-azaacene molecules in which two B <- N units were introduced at different positions. Although the dibenzo-azaacene skeleton is fully pi-conjugated, the effect of B <- N unit on the electronic structures of the adjacent rings is much stronger than that of the distant rings. As a result, the three molecules with isomerized B <- N incorporation patterns possess different electronic structures and exhibit tunable opto-electronic properties. Among the three molecules, the centrosymmetrical molecule exhibits higher LUMO/HOMO energy levels than those of the two axisymmetrical molecules. When used as the active layer in organic field-effect transistors (OFETs), while the two axisymmetrical molecules show unipolar electron transporting property, the centrosymmetrical molecule exhibits ambipolar hole and electron transporting behavior. This work not only deepens our understanding on organoboron pi-conjugated molecules, but also indicates a new strategy to tune opto-electronic properties of organic semiconductors for excellent device performance.

Automated summary

Incorporating B<-N units into pi-conjugated systems is an effective strategy to design organic small molecules and polymers with intriguing opto-electronic properties. The position of the B<-N units significantly influences the electronic structures of adjacent rings, leading to tunable opto-electronic properties of the molecules. Organoboron pi-conjugated molecules show potential for use in organic semiconductors for excellent device performance.