Materials exhibiting thermally activated delayed fluorescence (TADF) have been extensively explored in the last decade. These emitters have great potential of being used in organic light-emitting diodes because they allow for high quantum efficiencies by utilizing triplet states via reverse intersystem crossing. In small molecules, this is done by spatially separating the highest occupied molecular orbital from the lowest unoccupied molecular orbital, forming an intramolecular charge-transfer (iCT) state and leading to a small energy difference between lowest excited singlet and triplet states (ΔE ST ). However, in polymer emitters, this is harder to achieve, and typical strategies usually include adding known TADF units as sidechains onto a polymer backbone. In a previous work, we proposed an alternative way to achieve a TADF polymer by repeating a non-TADF unit, polymerizing it via electron-donating carbazole moieties. The extended conjugation on the backbone reduced the ΔE ST and allowed for an efficient TADF polymer. In this work, we present a more in-depth study of the shift from a non-TADF monomer to TADF oligomers. The monomer shows non-TADF emission, and we find the delayed emission to be of triplet−triplet annihilation origin. An iCT state is formed already in the dimer, leading to a much more efficient TADF emission. This is confirmed by an almost two-fold increase of photoluminescence quantum yield, a decrease in the delayed luminescence lifetime, and the respective spectral lineshapes of the molecules.
A pair of hole‐conducting polymers comprising 3,6‐linked carbazole and meta‐linked anisole derivatives having solubilizing moieties to enable their solution processability, and complementarily reactive side‐groups (azide and alkyne) for cross‐linking, are synthesized and characterized. The polymers can be cross‐linked either by thermal annealing at relatively low temperatures in the 85–110 °C range, or by UV irradiation. A general applicability of the latter for a photolithographic patterning of the hole conducting polymer is proven. The polymers have an ionization potential (IP) of 5.8 eV, close to the IP of a small molecule hole‐conductor tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA). In combination with a strong dopant hexacyano‐trimethylene‐cyclopropane (CN6CP), but not with commercial 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), the polymers can be efficiently p‐doped to increase their conductivity by 5–6 orders of magnitude, as measured in devices with a lateral setup. Taken together, these characteristics suggest that the synthesized polymers are promising candidates for their use in solution‐processable organic light‐emitting diodes as hole‐injection layer and hole‐transporting layer materials, which will be verified in the upcoming work.
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