Anthracenedicarboximide-based semiconductors for air-stable, n-channel organic thin-film transistors: Materials design, synthesis, and structural characterization

A family of six n-channel organic semiconductors (1-6) based on the N,N'-dialkyl-2,3:6,7-anthracenedicarboximide (ADI) core was synthesized and characterized. These new semiconductors are functionalized with n-octyl (-n-C ₈H ₁₇), 1H,1H-perfluorobutyl (-n-CH ₂C ₃F ₇), cyano (-CN), and bromo (-Br) substituents, which results in wide HOMO and LUMO energy variations (∼1 eV) but negligible optical absorbance (λ _max = 418-436 nm) in the visible region of the solar spectrum. Organic thin-film transistors (OTFTs) were fabricated via semiconductor vapor-deposition, and the resulting devices exhibit exclusively electron transport with good carrier mobilities (μ _e) of 10 ^-3 to 0.06 cm ² V ^-1 s ^-1. Within this semiconductor family, cyano core-substitution plays a critical role in properly tuning the LUMO energy to enable good electron transport in ambient conditions while maintaining a low level of ambient doping (i.e., low I _off). Core-cyanated ADIs 3 and 6 exhibit air-stable TFT device operation with electron mobilities up to 0.04 cm ² V ^-1 s ^-1 in air. Very high current on/off ratios of >10 ⁷ are measured with positive threshold voltages (V _th = 5-15 V) and low off currents (I _off = 10 ^-9 to 10 ^-12 A). Single-crystal structures of N,N'-1H,1H-perfluorobutyl ADIs 5 and 6 exhibit slipped-stack cofacial crystal packing with close π-π stacking distances of ∼3.2 Å. Additionally, close intermolecular interactions between imide-carbonyl oxygen and anthracene core-hydrogen are identified, which lead to the assembly of highly planar lamellar layers. Analysis of the air-stability of 1-6 thin films suggests that air-stability is mainly controlled by the LUMO energetics, and an electrochemical threshold of E _red1 = -0.3 to -0.4 V is estimated to stabilize n-channel transport in this family of materials.