N-Type Organic Semiconductors Based on π-Deficient Pentacenequinones: Synthesis, Electronic Structures, Molecular Packing, and Thin Film Transistors

Quinones are well-known as organic oxidizing reagents in organic synthesis and biological systems, but their ability of accepting electrons was rarely explored in connection with n-type organic semiconductors. Here, we report a comprehensive study on two groups of pi-deficient pentacenequinones, fluorinated pentacenequinones and N-heteropentacenequinones, highlighting their electronic structures, molecular packing, and n-channel thin film transistors. It is found that replacing H atoms of pentacenequinone with F atoms or replacing C atoms with N can lower the lowest unoccupied molecular orbital (LUMO) energy level of pentacenequinone to yield n-type organic semiconductors with the field effect mobility up to higher than 0.1 cm(2)V(-1)s(-1) in thin film transistors. A comparison between the two groups of quinones in terms of their electronic structures and molecular packing has led to interesting findings on the roles of electron-withdrawing moieties in tuning frontier molecular orbitals and pi-stacking. Another interesting finding on the molecular packing is the quadruple weak hydrogen bonds, which link the neighboring pi-stacks of quinones. This study suggests that pi-deficient quinones would be a general design for n-type organic semiconductors.