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  4. Getting the Right Twist: Influence of Donor-Acceptor Dihedral Angle on Exciton Kinetics and Singlet-Triplet Gap in Deep Blue Thermally Activated Delayed Fluorescence Emitter
 
research article

Getting the Right Twist: Influence of Donor-Acceptor Dihedral Angle on Exciton Kinetics and Singlet-Triplet Gap in Deep Blue Thermally Activated Delayed Fluorescence Emitter

Weissenseel, Sebastian
•
Drigo, Nikita A.  
•
Kudriashova, Liudmila G.
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November 14, 2019
Journal Of Physical Chemistry C

Here, a novel deep blue emitter SBABz4 for use in organic light-emitting diodes (OLED) is investigated. The molecular design of the emitter enables thermally activated delayed fluorescence (TADF), which we examine by temperature-dependent time-resolved electroluminescence (trEL) and photoluminescence (trPL). We show that the dihedral angle between donor and acceptor strongly affects the oscillator strength of the charge transfer state alongside the singlet-triplet gap. The angular dependence of the singlet-triplet gap is calculated by time-dependent density functional theory (TD-DFT). A gap of 15 meV is calculated for the relaxed groundstate configuration of SBABz4 with a dihedral angle between the donor and acceptor moieties of 86 degrees. Surprisingly, an experimentally obtained energy gap of 72 +/- 5 meV can only be explained by torsion angles in the range of 70-75 degrees. Molecular dynamics (MD) simulations showed that SBABz4 evaporated at high temperature acquires a distribution of torsion angles, which immediately leads to the experimentally obtained energy gap. Moreover, the emitter orientation anisotropy in a host shows an 80% ratio of horizontally oriented dipoles, which is highly desirable for efficient light outcoupling. Understanding intramolecular donor-acceptor geometry in evaporated films is crucial for OLED applications, because it affects oscillator strength and TADF efficiency.

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Type
research article
DOI
10.1021/acs.jpcc.9b08269
Web of Science ID

WOS:000497260100055

Author(s)
Weissenseel, Sebastian
Drigo, Nikita A.  
Kudriashova, Liudmila G.
Schmid, Markus
Morgenstern, Thomas
Lin, Kun-Han  
Prlj, Antonio  
Corminboeuf, Clemence  
Sperlich, Andreas
Bruetting, Wolfgang
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Date Issued

2019-11-14

Publisher

AMER CHEMICAL SOC

Published in
Journal Of Physical Chemistry C
Volume

123

Issue

45

Start page

27778

End page

27784

Subjects

Chemistry, Physical

•

Nanoscience & Nanotechnology

•

Materials Science, Multidisciplinary

•

Chemistry

•

Science & Technology - Other Topics

•

Materials Science

•

external quantum efficiency

•

diodes

•

simulation

•

molecules

•

energy

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
GMF  
LCMD  
LCPT  
Available on Infoscience
December 4, 2019
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/163531
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