Effects of donor position and multiple charge transfer pathways in asymmetric pyridyl-sulfonyl TADF emitters

Haykir G., AYDEMİR M., Tekin A., Tekin E., Danos A., YÜKSEL F., ...Daha Fazla

MATERIALS TODAY COMMUNICATIONS, cilt.31, 2022 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 31
  • Basım Tarihi: 2022
  • Doi Numarası: 10.1016/j.mtcomm.2022.103550
  • Dergi Adı: MATERIALS TODAY COMMUNICATIONS
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Compendex, INSPEC
  • Anahtar Kelimeler: Dual emission, TADF, Phenothiazine &amp, carbazole, ACTIVATED DELAYED FLUORESCENCE, CROSS-COUPLING REACTIONS, WHITE-LIGHT EMISSION, DENSITY FUNCTIONALS, THERMOCHEMISTRY, EXCHANGE, STATES
  • İstanbul Teknik Üniversitesi Adresli: Evet

Özet

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.