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

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.