Azaquinoid-Based High Spin Open-Shell Conjugated Polymer for n-Type Organic Field-Effect Transistors

Abstract

An open-shell quinoidal conjugated polymer exhibiting n-type semiconducting behavior is successfully synthesized and characterized. An electron-deficient azaaromatic unit is proven to reduce the energy levels of frontier orbitals via the electronegative nitrogen atom and steric hindrance within the polymer backbone. A synthesized azaquinoidal bithiophene (azaQuBT) is a quinoidal bithiophene that is end-functionalized with a pyridine ring. The open-shell quinodial conjugated polymer, poly(azaquinoidal bithiophene-thiophene), PazaQuBT-T, is synthesized using azaQuBT and thiophene. The extended quinoidal building block, which has an open-shell diradical character, induces low bandgaps, redox amphoterism, and high-spin-induced paramagnetic behavior of the resulting polymer. PazaQuBT-T achieves ambipolar charge-transport behavior in organic field-effect transistor (OFET) devices. Through a PEIE treatment onto the contact electrode, PazaQuBT-based OFETs exhibit unipolar n-channel operation with electron mobility up to 0.98 cm(2) V-1 s(-1). This work demonstrates the development of novel open-shell conjugated polymers with high-spin characteristics and n-type semiconducting property.