TY - JOUR
T1 - Effects of donor position and multiple charge transfer pathways in asymmetric pyridyl-sulfonyl TADF emitters
AU - Haykir, Gulcin
AU - Aydemir, Murat
AU - Tekin, Adem
AU - Tekin, Emine
AU - Danos, Andrew
AU - Yuksel, Fatma
AU - Hizal, Gurkan
AU - Monkman, Andrew P.
AU - Turksoy, Figen
N1 - Publisher Copyright:
© 2022 Elsevier Ltd
PY - 2022/6
Y1 - 2022/6
N2 - We have designed and synthesized a pair of highly asymmetric D-aA-D′ type pyridyl-sulfonyl based isomers comprising phenothiazine (PTZ) and carbazole (Cz) donor units, which are able to emit thermally activated delayed fluorescence. PTZ-pS4-Py-2Cz and PTZ-mS4-Py-2Cz both possess spatial separation of HOMO/LUMO on the donor and acceptor moieties, resulting in small calculated singlet–triplet energy gaps (~0.25 eV). Both isomers exhibit dual emission, which is attributed to charge transfer states associated with the Cz and PTZ moieties at higher and lower energies, respectively. Photoluminescence quantum yields and time-resolved emission decays show significant differences for the two isomers, with the para- isomer exhibiting more efficient emission and stronger delayed fluorescence than the meta- isomer – in strong contrast to recently reported analogous Cz-Cz D-aA-D isomers. The findings clearly show that the interconversion of triplets via the rISC mechanism is promoted when parallel Cz and PTZ charge transfer states are allowed to interact, explaining the improved performance of the Cz-PTZ materials compared to the previous Cz-Cz ones. Finally, moderate device performance was achieved in warm-yellowish (CIE; 0.41; 0.53 & 0.49; 0.48) non-doped OLEDs, which exhibited 0.5% & 1.9% maximum external quantum efficiencies for the meta- and para- isomers, respectively.
AB - We have designed and synthesized a pair of highly asymmetric D-aA-D′ type pyridyl-sulfonyl based isomers comprising phenothiazine (PTZ) and carbazole (Cz) donor units, which are able to emit thermally activated delayed fluorescence. PTZ-pS4-Py-2Cz and PTZ-mS4-Py-2Cz both possess spatial separation of HOMO/LUMO on the donor and acceptor moieties, resulting in small calculated singlet–triplet energy gaps (~0.25 eV). Both isomers exhibit dual emission, which is attributed to charge transfer states associated with the Cz and PTZ moieties at higher and lower energies, respectively. Photoluminescence quantum yields and time-resolved emission decays show significant differences for the two isomers, with the para- isomer exhibiting more efficient emission and stronger delayed fluorescence than the meta- isomer – in strong contrast to recently reported analogous Cz-Cz D-aA-D isomers. The findings clearly show that the interconversion of triplets via the rISC mechanism is promoted when parallel Cz and PTZ charge transfer states are allowed to interact, explaining the improved performance of the Cz-PTZ materials compared to the previous Cz-Cz ones. Finally, moderate device performance was achieved in warm-yellowish (CIE; 0.41; 0.53 & 0.49; 0.48) non-doped OLEDs, which exhibited 0.5% & 1.9% maximum external quantum efficiencies for the meta- and para- isomers, respectively.
KW - Dual emission
KW - Phenothiazine & carbazole
KW - TADF
UR - http://www.scopus.com/inward/record.url?scp=85129515960&partnerID=8YFLogxK
U2 - 10.1016/j.mtcomm.2022.103550
DO - 10.1016/j.mtcomm.2022.103550
M3 - Article
AN - SCOPUS:85129515960
SN - 2352-4928
VL - 31
JO - Materials Today Communications
JF - Materials Today Communications
M1 - 103550
ER -