Controllable Singlet-Triplet Energy Splitting of Graphene Quantum Dots through Oxidation: From Phosphorescence to TADF.
basic_science · Level V
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- Record sourced from PubMed, PMID 32537946.
- Also identified by DOI 10.1002/adma.202000936.
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Abstract
Long-lived afterglow emissions, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), are beneficial in the fields of displays, bioimaging, and data security. However, it is challenging to realize a single material that simultaneously exhibits both RTP and TADF properties with their relative strengths varied in a controlled manner. Herein, a new design approach is reported to control singlet-triplet energy splitting (∆E<sub>ST</sub> ) in graphene quantum dots (GQD)/graphene oxide quantum dots (GOQDs) by varying the ratio of oxygenated carbon to sp<sup>2</sup> carbon (γ<sub>OC</sub> ). It is demonstrated that ∆E<sub>ST</sub> decreases from 0.365 to 0.123 eV as γ<sub>OC</sub> increases from 4.63% to 59.6%, which in turn induces a dramatic transition from RTP to TADF. Matrix-assisted stabilization of triplet excited states provides ultralong lifetimes to both RTP and TADF. Embedded in boron oxynitride, the low oxidized (4.63%) GQD exhibits an RTP lifetime (τ<sup>T</sup> <sub>avg</sub> ) of 783 ms, and the highly oxidized (59.6%) GOQD exhibits a TADF lifetime (τ<sup>DF</sup> <sub>avg</sub> ) of 125 ms. Furthermore, the long-lived RTP and TADF materials enable the first demonstration of anticounterfeiting and multilevel information security using GQD. These results will open up a new approach to the engineering of singlet-triplet splitting in GQD for controlled realization of smart multimodal afterglow materials.