6,6′-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′-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 cm² V⁻¹ s⁻¹, of which the devices based on 2 demonstrated an electron mobility of up to 0.52 cm² 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 cm² V⁻¹ s⁻¹ and 0.029 cm² 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′-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.