6,6 0 -Diaryl-substituted biazulene diimides for solution-processable high-performance n-type organic semiconductors†

Abstract

Azulene, a non-benzenoid aromatic hydrocarbon, is a promising building block for constructing organic optoelectronic materials. Herein, a series of 6,6 0 -diaryl-substituted biazulene diimides (1-5) are designed and synthesized for solution-processable organic semiconductors. These compounds exhibited excellent electron transport properties with fine-tuned molecular energy levels (HOMO: 5.68 to 6.04 eV; LUMO: 3.63 to 3.73 eV). Bottom-gate-top-contact organic field effect transistors (OFETs) based on compounds 1-3 and 5 displayed unipolar n-type semiconducting properties with optimized average electron mobilities of 0.12-0.45 cm 2 V 1 s 1 , of which the devices based on 2 demonstrated an electron mobility of up to 0.52 cm 2 V 1 s 1 , the highest electron mobilities for azulene-based organic semiconductors and also among the highest values for solution-processable n-channel OFETs. Devices based on 4 showed ambipolar FET performance with electron and hole mobilities of 0.31 cm 2 V 1 s 1 and 0.029 cm 2 V 1 s 1 , respectively. The ambipolar charge transport behavior of 4 is due to its higher HOMO energy level (5.68 eV) than the others (5.78 to 6.04 eV). The excellent electron transport ability of compounds 1-5 might be attributed to the dense molecular packing induced by the dipolar moment of the azulene units as revealed by single crystal analysis. Besides, compounds 2 and 5 were used as electron acceptors for organic photovoltaic devices, and an average power conversion efficiency of about 1.3% was obtained for their respective blend thin films with electron donor PTB7-Th. The results demonstrate that 6,6 0 -diaryl-substituted biazulene diimides are promising solution-processable n-type organic semiconductors, and the azulene unit has great potential for constructing excellent organic optoelectronic materials.