Journal
ADVANCED MATERIALS
Volume 32, Issue 45, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adma.202003911
Keywords
afterglow; charge recombination; charge separation; long-persistent luminescence (LPL); organic long-persistent luminescence (OLPL); thermally activated delayed fluorescence (TADF)
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Funding
- EPSRC [EP/P010482/1, EP/R035164/1, EP/L017008/1]
- Leverhulme Trust Research Grant [RPG-2017-231]
- Japan Science and Technology Agency (JST), ERATO, Adachi Molecular Exciton Engineering Project, under JST ERATO Grant [JPMJER1305]
- JSPS Core-to-Core Program
- JSPS KAKENHI [JP18H02049, JP18H04522]
- International Institute for Carbon Neutral Energy Research (WPI-I2CNER) - Ministry of Education, Culture, Sports, Science and Technology (MEXT)
- China Scholarship Council [201708060003, 201703780004, 201806890001]
- Newton Fellowship [NF171163]
- EPSRC [EP/L017008/1, EP/P010482/1, EP/R035164/1, EP/J01771X/1, EP/R010595/1] Funding Source: UKRI
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Organic long-persistent luminescence (OLPL) is one of the most promising methods for long-lived-emission applications. However, present room-temperature OLPL emitters are mainly based on a bimolecular exciplex system which usually needs an expensive small molecule such as 2,8-bis(diphenyl-phosphoryl)dibenzo[b,d]thiophene (PPT) as the acceptor. In this study, a new thermally activated delayed fluorescence (TADF) compound, 3-(4-(9H-carbazol-9-yl)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (CzPhAP), is designed, which also shows OLPL in many well-known hosts such as PPT, 2,2 ',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), and poly(methyl methacrylate) (PMMA), without any exciplex formation, and its OLPL duration reaches more than 1 h at room temperature. Combining the low cost of PMMA manufacture and flexible designs of TADF molecules, pure organic, large-scale, color tunable, and low-cost room-temperature OLPL applications become possible. Moreover, it is found that the onset of the 77 K afterglow spectra from a TADF-emitter-doped film is not necessarily reliable for determining the lowest triplet state energy level. This is because in some TADF-emitter-doped films, optical excitation can generate charges (electron and holes) that can later recombine to form singlet excitons during the phosphorescence spectrum measurement. The spectrum taken in the phosphorescence time window at low temperature may consequently consist of both singlet and triplet emission.
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