π-Extended indoloquinoxaline functionalized triarylamines with ethynyl and tetracyanobutadiene bridges for p-channel and ambipolar OFETs

Abstract

New D–A indoloquinoxaline functionalized triarylamine semiconductors with various π-bridging motifs were designed and synthesized for p-channel and ambipolar organic transistors. This is the first attempt to use indoloquinoxaline as an effective inbuilt donor system for air-stable organic field-effect transistors (OFETs). The structure–property relationship of triarylamine–indoloquinoxalines (TAA–IQ) is systematically studied in terms of their electrochemical, photophysical, structural, and electrical characteristics. Bottom-gate top contact OFET devices fabricated using TAA–IQ with an ethynyl spacer exhibited p-channel characteristics with a field-effect mobility of 1.50 cm² V⁻¹ s⁻¹ and an on/off current ratio of 10⁵. The electron-deficient TCBD group, as a central acceptor in the TAA–IQ architecture, exhibited low-lying LUMO energy levels at around −3.96 eV, allowing easy electron injection and stable electron transfer under ambient conditions. The TCBD bridged TAA–IQ compound exhibited ambipolar characteristics with the highest hole mobility μ_h of 0.35 cm² V⁻¹ s⁻¹, an on/off current ratio of up to 10⁶ and an electron mobility μ_e of 2.1 cm² V⁻¹ s⁻¹. Remarkably, the devices based on IQ–TAA with TCBD showed a much better performance than those based on the related ambipolar compounds.