Aryl-Diazafluoren(on)es for Organic Optoelectronics: Toward Air-Stable N‑type OFETs and Gas Sensors

While fluorene-containing materials are widely used in organic optoelectronics as bright emitters and hole semiconductors, their diazafluorene analogues have been poorly explored, though their nitrogen atoms could result in electron transport and bring sensory abilities. Here, we report the synthesis, characterization, and detailed study of a series of 4,5-diazafluorene-derivatives with different donor/acceptor substituents and organic semiconductors based on these molecules. The crystal structures of all the materials were solved by X-ray diffraction, indicating the presence of extensive π-stacking and anisotropic charge-transfer pathways. The materials were applied as active layers in single-crystal and thin-film organic field-effect transistors (OFETs) demonstrating air-stable electron transport with charge-carrier mobility up to 0.02 cm2/(V s) for (2,7-diphenyl-4,5-diazafluorene-9-ylidene)malononitrile (P-DAF-CN). Moreover, P-DAF-CN thin-film OFETs were employed as gas sensors demonstrating a sensor response toward sub-ppm concentrations of hydrogen sulfide. 4,5-Diazafluorene-based materials are shown to be promising organic semiconductors on the way to high-performance air-stable n-channel OFETs and electronic nose applications.