Through-Space Charge-Transfer Thermally Activated Delayed Fluorescence Alternating Donor–Acceptor Copolymers for Nondoped Solution-Processable OLEDs

A series of donor–acceptor alternating copolymers with Mn ≤ 12,000 g mol–1 and moderate polydispersity (Đ = 1.5–2.5) were synthesized via RAFT copolymerization of styrene-based donor monomers and maleimide-type acceptor monomers in the presence of S-dodecyl-S′-(α,α′-dimethyl-α″-acetic acid)trithiocarbonate as a chain transfer agent. It was shown that synthesized alternating copolymers were characterized by high thermal stability (Td5 = 375–465 °C), and most of them exhibited exciplex emission via the through-space charge-transfer (TSCT) mechanism and displayed aggregation-induced emission. The color of the emission of synthesized copolymers largely depended on the nature of the acceptor monomer and could be changed from blue to orange depending on the copolymer structure. These copolymers in solid state demonstrated delayed fluorescence in the range between 0.35 and 6.2 μs and moderate photoluminescence quantum yield (2.12–6.32%) in air. Multicolor host-free solution-processable TADF OLEDs using synthesized alternating copolymers as emitters were fabricated, which showed good stability of electroluminescence spectra at different voltages. The highest external quantum efficiency of 7.84% was reached for the green emitting device.