Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters

Research output: Contribution to journalArticle



  • Marc K. Etherington
  • Flavio Franchello
  • Jamie Gibson
  • Thomas Northey
  • Jose Santos
  • Jonathan S. Ward
  • Heather F. Higginbotham
  • Przemyslaw Data
  • Aleksandra Kurowska
  • Paloma Lays Dos Santos
  • David R. Graves
  • Andrei S. Batsanov
  • Fernando B. Dias
  • Martin R. Bryce
  • Thomas J. Penfold
  • Andrew P. Monkman


Original languageEnglish
Article number 14987
JournalNature Communications
Publication statusPublished - 13 Apr 2017
Publication type

Research output: Contribution to journalArticle


Regio- and conformational isomerization are fundamental in chemistry, with profound effects upon physical properties, however their role in excited state properties is less developed. Here two regioisomers of bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide, a donor–acceptor–donor (D–A–D) thermally-activated delayed fluorescence (TADF) emitter, are studied. 2,8-bis(10H-phenothiazin-10-yl)dibenzo[b,d]thiophene-S,S-dioxide exhibits only one quasi-equatorial conformer on both donor sites, with charge-transfer (CT) emission close to the local triplet state leading to efficient TADF via spin-vibronic coupling. However, 3,7-bis(10H-phenothiazin-10 yl)dibenzo[b,d]thiophene-S,S-dioxide displays both a quasi-equatorial CT state and a higher-energy quasi-axial CT state. No TADF is observed in the quasi-axial CT emission. These two CT states link directly to the two folded conformers of phenothiazine. The presence of the low-lying local triplet state of the axial conformer also means that this quasi-axial CT is an effective loss pathway both photophysically and in devices. Importantly, donors or acceptors with more than one conformer have negative repercussions for TADF in organic light-emitting diodes.

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