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Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules
The Journal of Physical Chemistry Letters, Volume: 9, Issue: 14, Pages: 4053 - 4058
Swansea University Author: Emrys Evans
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Electrically injected charge carriers in organic light-emitting devices (OLEDs) undergo recombination events to form singlet and triplet states in a 1:3 ratio, representing a fundamental hurdle for achieving high quantum efficiency. Dopants based on thermally activated delayed fluorescence (TADF) ha...
|Published in:||The Journal of Physical Chemistry Letters|
American Chemical Society (ACS)
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Electrically injected charge carriers in organic light-emitting devices (OLEDs) undergo recombination events to form singlet and triplet states in a 1:3 ratio, representing a fundamental hurdle for achieving high quantum efficiency. Dopants based on thermally activated delayed fluorescence (TADF) have emerged as promising candidates for addressing the spin statistics issue in OLEDs. In these materials, reverse singlet–triplet intersystem crossing (rISC) becomes efficient, thereby activating luminescence pathways for weakly emissive triplet states. However, despite a growing consensus that torsional vibrations facilitate spin–orbit-coupling- (SOC-) driven ISC in these molecules, there is a shortage of experimental evidence. We use transient electron spin resonance and theory to show unambiguously that SOC interactions drive spin conversion and that ISC is a dynamic process gated by conformational fluctuations for benchmark carbazolyl–dicyanobenzene TADF emitters.
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E.W.E., N.C.G. and R.H.F. would like to thank the EPSRC for funding (EP/M01083X/1, EP/M005143/1). Y.P. is grateful to The Swedish Research Council VR2015-00436 for a postdoc grant. W.K.M. is supported by the EPSRC grant EP/L011972/ 1 for CAESR (Centre for Advanced Electron Spin Resonance). T.J.H.H. thanks Jesus College, Cambridge, for a Research Fellowship. DJNC acknowledges the Royal Society for a University Research Fellowship. The work in Mons was supported by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 646176 (EXTMOS project) and by Belgian National Fund for Scientific Research (FNRS/F.R.S.). Computational resources have been provided by the Consortium des É quipements de Calcul Intensif (CÉ CI), funded by F.R.S.-FNRS under Grant No. 2.5020.11 as well as the Tier-1 supercomputer of the Fedé ration Wallonie-Bruxelles, funded by the Walloon Region ́
under Grant Agreement No. 1117545.