Dielectric control of reverse intersystem crossing in thermally activated delayed fluorescence emitters

Alexander J. Gillett, Anton Pershin, Raj Pandya, Sascha Feldmann, Alexander J. Sneyd, Antonios M. Alvertis, Emrys W. Evans, Tudor H. Thomas, Lin Song Cui, Bluebell H. Drummond, Gregory D. Scholes, Yoann Olivier, Akshay Rao, Richard H. Friend, David Beljonne

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Thermally activated delayed fluorescence enables organic semiconductors with charge transfer-type excitons to convert dark triplet states into bright singlets via reverse intersystem crossing. However, thus far, the contribution from the dielectric environment has received insufficient attention. Here we study the role of the dielectric environment in a range of thermally activated delayed fluorescence materials with varying changes in dipole moment upon optical excitation. In dipolar emitters, we observe how environmental reorganization after excitation triggers the full charge transfer exciton formation, minimizing the singlet–triplet energy gap, with the emergence of two (reactant-inactive) modes acting as a vibrational fingerprint of the charge transfer product. In contrast, the dielectric environment plays a smaller role in less dipolar materials. The analysis of energy–time trajectories and their free-energy functions reveals that the dielectric environment substantially reduces the activation energy for reverse intersystem crossing in dipolar thermally activated delayed fluorescence emitters, increasing the reverse intersystem crossing rate by three orders of magnitude versus the isolated molecule.

Original languageEnglish (US)
Pages (from-to)1150-1157
Number of pages8
JournalNature Materials
Issue number10
StatePublished - Oct 2022

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • General Materials Science


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