Journal
ADVANCED MATERIALS
Volume 33, Issue 39, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adma.202101844
Keywords
non-radiative loss; phenanthroimidazole; room-temperature phosphorescence; triplet emission
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Funding
- China Scholarship Council [201706375057, 201506160049]
- Graduate Academy of TU Dresden
- National Natural Science Foundation of China [21506258, 21703023]
- European Research Council (ERC) under the European Union [679213]
- Projekt DEAL
- European Research Council (ERC) [679213] Funding Source: European Research Council (ERC)
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This research demonstrates the stabilization of excited states in organic molecules by substituting a hydrogen atom with an N-phenyl ring, leading to efficient and ultralong afterglow phosphorescence at room temperature. Further modification of the N-phenyl ring with halogen atoms affects the afterglow lifetime and quantum yield. An anticounterfeiting device with a time-dependent Morse code feature for data encryption is demonstrated based on these emitters.
Persistent luminescence from triplet excitons in organic molecules is rare, as fast non-radiative deactivation typically dominates over radiative transitions. This work demonstrates that the substitution of a hydrogen atom in a derivative of phenanthroimidazole with an N-phenyl ring can substantially stabilize the excited state. This stabilization converts an organic material without phosphorescence emission into a molecular system exhibiting efficient and ultralong afterglow phosphorescence at room temperature. Results from systematic photophysical investigations, kinetic modeling, excited-state dynamic modeling, and single-crystal structure analysis identify that the long-lived triplets originate from a reduction of intrinsic non-radiative molecular relaxations. Further modification of the N-phenyl ring with halogen atoms affects the afterglow lifetime and quantum yield. As a proof-of-concept, an anticounterfeiting device is demonstrated with a time-dependent Morse code feature for data encryption based on these emitters. A fundamental design principle is outlined to achieve long-lived and emissive triplet states by suppressing intrinsic non-radiative relaxations in the form of molecular vibrations or rotations.
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