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

Abstract

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-C₈H₁₇), 1H,1H-perfluorobutyl (-n-CH₂C₃F₇), 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 cm² 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 cm² V⁻¹ s⁻¹ in air. Very high current on/off ratios of >10⁷ 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.