Journal
NATURE COMMUNICATIONS
Volume 12, Issue 1, Pages -Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41467-021-26689-8
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Funding
- Simons Foundation [601946]
- EPSRC [EP/M01083X/1, EP/M005143/1, EP/L01551X/1]
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme [670405]
- Swedish Energy Agency [EM-48594-1]
- Swedish Research Council [VR-2017-05285]
- Aix Marseille Universite
- CNRS
- Basque Government [PIBA19-0004]
- Spanish Government MINECO/FEDER [PID2019-109555GB-I00]
- European Union's Horizon 2020 research and innovation programme under Marie Skodowska Curie Grant [722651]
- Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS) [2.5020.11]
- Tier-1 supercomputer of the Fede'ration Wallonie-Bruxelles
- Walloon Region [1117545]
- FRS-FNRS [F.4534.21]
- 'Fonds pour la formation a la Recherche dans l'Industrie et dans l'Agriculture' (F.R.I.A.) of the F.R.S.-F.N.R.S
- Vinnova [2017-05285] Funding Source: Vinnova
- Swedish Research Council [2017-05285] Funding Source: Swedish Research Council
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The study shows that access to inter-CT states in BF2, even at low doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low Delta E-ST in organic DF emitters.
Engineering a low singlet-triplet energy gap (Delta E-ST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 x 10(5) cm(-1)) and a relatively large Delta E-ST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 mu s), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a similar to 24 ns timescale and have an average electron-hole separation of >= 1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low Delta E-ST in organic DF emitters.
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