Thiadiazolobenzotriazole-Based Donor–Acceptor Terpolymers That Can Be Processed from Green Solvents and Deliver 950 nm Emission in Light-Emitting Electrochemical Cells

Abstract

Organic semiconductors that deliver emission with a wavelength exceeding 900 nm can enable a wide range of applications, but the unfortunate fact is that only a small number of such emitters have been synthesized and have demonstrated emissive function in devices. Here, this issue is addressed through the design and synthesis of two terpolymers that comprise a low energy-gap thiophene-thiadiazolobenzotriazole (TBTzTD) donor-acceptor unit as the minority guest incorporated in a majority donor-acceptor conjugated copolymer host, being either thiophene-quinoxaline (TQ) or thiophene-difluoroquinoxaline (TQ2F). These terpolymers are further endowed with high solubility in benign hydrophilic solvents through the grafting of branched oligo-(ethylene glycol) side chains onto the quinoxaline unit. The application function of the terpolymer emitters is demonstrated through their implementation in light-emitting electrochemical cells (LECs). It is notable from a sustainability perspective that the emitter is metal free and that the single-layer LEC active material is cast from an environmentally benign water:ethanol solvent blend. From an application perspective, it is attractive that the terpolymer-LEC devices feature a very fast turn-on to significant radiance at low voltage and that they deliver emission with a peak wavelength of 935 nm with TQ-TBTzTD as the emitter and 950 nm with TQ2F-TBTzTD as the emitter.