Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 12, Issue 11, Pages 2712-2720Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.1c00094
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Funding
- National Institutes of Health [R01GM135392]
- Oklahoma Center for the Advancement of Science and Technology [HR18-130]
- Office of the Vice President of Research at the University of Oklahoma (OU)
- College of Art and Sciences at the University of Oklahoma (OU)
- National Natural Science Foundation of China [22003030, 21573177, 21833006, 21788102]
- Ministry of Science and Technology of China through the National Key RD Plan [2017YFA0204501]
- China Postdoctoral Science Foundation [2020M670280]
- Shuimu Tsinghua Scholar Program
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Researchers have designed a TADF molecule m-Cz-BNCz that emits pure green light and achieved an external quantum efficiency of 27%. Through the use of advanced electronic structure analysis tools, they have identified the molecular design principles and potential applications for other TADF and functional dye molecules.
Recently, Wang and co-workers carried out frontier molecule orbital engineering in the design of m-Cz-BNCz, a thermally activated delayed fluorescence (TADF) molecule that emits pure green light at an external quantum efficiency of 27%. To further understand the underlying molecular design principles, we employed four advanced electronic structure analysis tools. First, an absolutely localized molecular orbitals (ALMO-) based analysis indicates an antibonding combination between the highest occupied molecular orbitals (HOMOs) of the donor 3,6-di-tert-butylcarbazole fragment and the acceptor BNCz fragment, which raises the HOMO energy and red-shifts the fluorescence emission wavelength. Second, excitation energy component analysis reveals that the S-1-T-1 gap is dominated by two-electron components of the excitation energies. Third, charge transfer number analysis, which is extended to use fragment-based Hirshfeld weights, indicates that the S-1 and T-1 excited states of m-Cz-BNCz (within time-dependent density functional theory) have notable charge transfer characters (27% for S-1 and 12% for T-1). This provides a balance between a small single-triplet gap and a substantial fluorescence intensity. Last, a vibrational reorganization energy analysis pinpoints the torsional motion between the BNCz and Cz moieties of m-Cz-BNCz as the source for its wider emission peak than that of p-Cz-BNCz. These four types of analyses are expected to be very valuable in the study and design of other TADF and functional dye molecules.
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