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

Abstract

A series of donor−acceptor alternating copolymers with M n ≤ 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 (T d5 = 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 solutionprocessable 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.

Polymerization-Mediated Through-Space Charge Transfer: An Emerging Strategy for Light-Emitting Materials

“…Significant AIE activity was again observed in the TSCT polymers containing acridan donor and triarylboron acceptors, synthesized by the same group. , These results indicated that the aggregation of the polymer chains may faciliate the excited state emission from the TSCT processes that are dependent on the D–A distance. In a recent study, another type of TSCT polymer was synthesized by alternating copolymerization of styrenic donor monomers and maleimide-derived acceptor monomers. AIE properties were also reported in these polymers, which further confirmed the aggregated-enhanced TSCT effect.…”

“…Overall, polymerization has been used as a robust and convenient tool to manipulate the donor-to-acceptor TSCT in the manner of monomer-to-monomer ,− (including side chain-to-side chain), end group-to-initiator, and monomer-to-initiator modes . By rational structural design, more diverse polymeric TSCT systems remain to be discovered based on the controlled polymerization-mediated TSCT strategy.…”

Unveiling the potential of nonconjugate linkers (sp3-cores) in through-space charge transfer emitters and host materials for thermally activated delayed fluorescence organic light emitting diodes

“…Kostjuk et al demonstrated the synthesis of 16 new styrene-based donor–acceptor alternating copolymers ( D1A1 to D4A4 ) for use as non-doped TADF emitters (Scheme 6). 66 These polymers were created through reversible addition–fragmentation chain-transfer (RAFT) copolymerization, resulting in an average molecular weight ( M n ) of approximately 12 000 g mol −1 and a moderate polydispersity index (PDI) ranging from 1.5 to 2.5. The donor monomers included styrene-based 6-dimethoxycarbazole, 9,9-dimethylacridane, and phenoxazine, whereas the acceptor monomers consisted of maleimide-tethered benzophenone and benzonitrile.…”

“…Molecules exhibiting TSCT, particularly those based on nonconjugated spacers, have considerable advantages. 49–77,90–99 These spacers disrupt the direct conjugation between donors and acceptors; thus, they are sophisticated in creating blue emitters and high triplet energy ( E T ) host materials. The use of various nonconjugate spacers, such as adamantane, 67,68 silane (Si), 69 cyclohexane, 62–65,70,71 vinyl, 75–77 and others, 52–61 offers a diverse toolkit for tailoring the properties of these materials.…”

Alternating Thermally Activated Delayed Fluorescence Copolymers Featuring Through-Space Charge Transfer for Efficient Electroluminescence

“…Nevertheless, it typically results in inevitable red-shifted emission and even the absence of TADF property. − Thanks to the efforts of researchers, a series of different kinds of nonconjugated alternating copolymers with poly­(maleic anhydride- alt -styrene), , poly­(maleimide- alt -styrene), , and poly­(maleic anhydride- alt -vinyl acetate) skeletons were successfully developed . Benefiting from this accurate sequence structure, the well-defined alternating copolymers exhibit advantageous properties such as the enhanced thermal stabilities and unexpectedly luminescent properties. − Unlike the random structures in conventional TSCT-based TADF copolymers, alternating polymerization would be more powerful to construct sequence-controlled alternating copolymers. , …”