Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules

Emrys W. Evans; Yoann Olivier; Yuttapoom Puttisong; William K. Myers; Timothy J.H. Hele; S. Matthew Menke; Tudor H. Thomas; Dan Credgington; David Beljonne; Richard H. Friend; Neil C. Greenham

doi:10.1021/acs.jpclett.8b01556

Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules

Emrys W. Evans, Yoann Olivier, Yuttapoom Puttisong, William K. Myers, Timothy J.H. Hele, S. Matthew Menke, Tudor H. Thomas, Dan Credgington, David Beljonne, Richard H. Friend, Neil C. Greenham

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Abstract

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.

Original language	English
Pages (from-to)	4053-4058
Number of pages	6
Journal	The Journal of Physical Chemistry Letters
Volume	9
Issue number	14
DOIs	https://doi.org/10.1021/acs.jpclett.8b01556
Publication status	Published - 19 Jul 2018
Externally published	Yes

Funding

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 Équipements de Calcul Intensif (CÉCI), funded by F.R.S.-FNRS under Grant No. 2.5020.11 as well as the Tier-1 supercomputer of the Fed́ eŕ ation Wallonie-Bruxelles, funded by the Walloon Region under Grant Agreement No. 1117545. D.B. is a FNRS Research Director. Y.O. acknowledges stimulating discussions with Prof. J. C. Sancho-Garcia from the University of Alicante and Prof. L. Muccioli from the University of Bologna.

Funders	Funder number
FNRS/F	2.5020.11
Horizon 2020 Framework Programme	646176
Waalse Gewest	1117545
Engineering and Physical Sciences Research Council	EP/M01083X/1, EP/M005143/1
Royal Society
Jesus College, University of Cambridge
Fonds De La Recherche Scientifique - FNRS
Vetenskapsrådet	EP/L011972/ 1, VR2015-00436

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Evans, E. W., Olivier, Y., Puttisong, Y., Myers, W. K., Hele, T. J. H., Menke, S. M., Thomas, T. H., Credgington, D., Beljonne, D., Friend, R. H., & Greenham, N. C. (2018). Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules. The Journal of Physical Chemistry Letters, 9(14), 4053-4058. https://doi.org/10.1021/acs.jpclett.8b01556

@article{46eb9bea95094d3292552308201c12ec,

title = "Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules",

abstract = "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.",

author = "Evans, \{Emrys W.\} and Yoann Olivier and Yuttapoom Puttisong and Myers, \{William K.\} and Hele, \{Timothy J.H.\} and Menke, \{S. Matthew\} and Thomas, \{Tudor H.\} and Dan Credgington and David Beljonne and Friend, \{Richard H.\} and Greenham, \{Neil C.\}",

year = "2018",

month = jul,

day = "19",

doi = "10.1021/acs.jpclett.8b01556",

language = "English",

volume = "9",

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journal = "The Journal of Physical Chemistry Letters",

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publisher = "American Chemical Society",

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Evans, EW, Olivier, Y, Puttisong, Y, Myers, WK, Hele, TJH, Menke, SM, Thomas, TH, Credgington, D, Beljonne, D, Friend, RH & Greenham, NC 2018, 'Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules', The Journal of Physical Chemistry Letters, vol. 9, no. 14, pp. 4053-4058. https://doi.org/10.1021/acs.jpclett.8b01556

TY - JOUR

T1 - Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules

AU - Evans, Emrys W.

AU - Olivier, Yoann

AU - Puttisong, Yuttapoom

AU - Myers, William K.

AU - Hele, Timothy J.H.

AU - Menke, S. Matthew

AU - Thomas, Tudor H.

AU - Credgington, Dan

AU - Beljonne, David

AU - Friend, Richard H.

AU - Greenham, Neil C.

PY - 2018/7/19

Y1 - 2018/7/19

N2 - 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.

AB - 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.

UR - https://www.scopus.com/pages/publications/85049350756

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SN - 1948-7185

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EP - 4058

JO - The Journal of Physical Chemistry Letters

JF - The Journal of Physical Chemistry Letters

IS - 14

ER -

Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules

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