Pyridyl Pyrrolide Boron Complexes: The Facile Generation of Thermally Activated Delayed Fluorescence and Preparation of Organic Light-Emitting Diodes

The electron positive boron atom usually does not contribute to the frontier orbitals for several lower‐lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light‐emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatiall...

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Published in:Angewandte Chemie (International ed.) 2016-02, Vol.55 (9), p.3017-3021
Main Authors: Shiu, Yi-Jiun, Cheng, Yung-Chen, Tsai, Wei-Lung, Wu, Chung-Chih, Chao, Chun-Tien, Lu, Chin-Wei, Chi, Yun, Chen, Yi-Ting, Liu, Shih-Hung, Chou, Pi-Tai
Format: Article
Language:English
Subjects:
Bearing
Boron
Charge transfer
Correlation
Delay
Diodes
Electron transitions
Emission
Energy
Energy gap
Fluorescence
Fragmentation
Fragments
Light effects
Light emitting diodes
Molecular orbitals
OLEDs
Orientation
photoluminescence
Polarity
thermally activated delay fluorescence
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Summary:The electron positive boron atom usually does not contribute to the frontier orbitals for several lower‐lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light‐emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatially separated with orthogonal orientation. On this basis, we prepared a series of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine. The new boron complexes show strong solvent‐polarity dependent charge‐transfer emission accompanied by a small, non‐negligible normal emission. The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔET‐S) and thereby the generation of thermally activated delay fluorescence (TADF). Reducing the gap: Using a boron atom as the spiro linker between an electron‐deficient pyridyl pyrrolide and an electron‐donating phenylcarbazolyl or triphenylamine fragment, boron complexes with a narrow HOMO–LUMO orbital overlap, small singlet–triplet energy gap (down to 38 meV), and strong thermally activated delayed fluorescence (TADF) were prepared. For the first time boron‐complex‐based OLEDs show a significant TADF contribution.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201509231