Journal
ADVANCED OPTICAL MATERIALS
Volume 4, Issue 10, Pages 1558-1566Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adom.201600304
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Funding
- National Basic Research Program of China (973 Program) [2013CB834805, 2015CB655002]
- National Natural Science Foundation of China [91433201, U1402273, 51573141, 51125013]
- Innovative Research Group of Hubei Province [2015CFA014]
- Fundamental Research Funds for the Central Universities of China [2042015kf0033, 2042015kf0007]
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Three isomeric phenanthroline compounds, namely o-PXZP, m-PXZP, and p-PXZP, are constructed by incorporating electron-donor phenoxazine unit into ortho-, meta-, or para-positions of a rigid electron-acceptor phenanthroline core. This approach functionalizes these compounds to exhibit thermally activated delayed fluorescence (TADF) characteristics with microsecond-scale photoluminescence (PL) lifetimes. Their thermal, electrochemical properties, emissive characteristics, and energy levels can be finely tailored through isomer engineering. The meta-and para-linking compounds (m-PXZP and p-PXZP) possess higher decomposition temperatures, deeper lowest unoccupied molecular orbital levels, higher PL quantum efficiencies, smaller singlet-triplet energy splitting, and reduced DF lifetimes relative to their ortho-disposition isomer (o-PXZP). Consequently, a green fluorescence organic light-emitting diode (OLED) based on m-PXZP achieves a maximum external quantum efficiency of 18.9%, and has a slow efficiency roll-off of 28% at the luminance of 1000 cd m(-2). Notably, m-PXZP-based device exhibits a nearly 100% utilization efficiency of electro-generated singlet and triplet excitons. These results demonstrate for the first time that phenanthroline derivatives can be employed as TADF emitters for high-efficiency OLEDs. The isomer engineering for TADF emitters provides a simple method to extend structure diversity of TADF emitters, and moreover it provides a flexible method to optimize optoelectronic properties and thereby manipulate electroluminescence performance.
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