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Issue 34, 2017
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Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

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Abstract

The field of organic light-emitting devices (OLEDs) has undergone a remarkable journey since its discovery by Tang and VanSlyke with an alternation of utilizing fluorescence and phosphorescence as the emitting vehicle. The latest generation of thermally activated delayed fluorescence (TADF) materials harvest triplet excited states back into the singlet manifold. This booming field has yielded a large array of new compounds as both emitters and hosts. This review is limited to TADF emitters utilizing at least one carbazole unit as a donor and organized according to the various acceptor building blocks such as cyanophenyl, pyridine, biphenyls, anthraquinone, phenyl(pyridine-2-yl)methanone, benzophenone, xanthon, sulfones, triazines, benzils, dicyanopyrazines, diazatriphenylene, and others. A survey of carbazole-containing host materials follows. Density functional theory (DFT) has carved out a significant role in allowing the theoretical prediction of ground state properties for materials applied in OLED technology. Time-dependent DFT extends the reach to model excited state properties important to rationalize the light-output in OLED technology. For TADF, two fundamental factors are of interest: significant separation of frontier molecular orbitals and minimal singlet–triplet energy gap (ΔEST). In this review, the utilization of DFT calculations to optimize geometries for the visualization of frontier molecular orbital separation was surveyed to find that the B3LYP/6-31G(d) level of theory is the overwhelmingly used approach. In addition, we review the more in-depth approaches to utilizing DFT and time-dependent DFT (TD-DFT) with optimized percentage Hartree–Fock (OHF) and long-range corrected hybrid functionals, tuning procedures and others in an attempt to best quantify the size of ΔEST as well as the nature of the triplet state as locally excited state (LE) and charge-transfer state (CT).

Graphical abstract: Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

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Publication details

The article was received on 16 May 2017, accepted on 10 Jul 2017 and first published on 11 Jul 2017


Article type: Review Article
DOI: 10.1039/C7TC02156A
Citation: J. Mater. Chem. C, 2017,5, 8622-8653
  • Open access: Creative Commons BY license
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    Perspective on carbazole-based organic compounds as emitters and hosts in TADF applications

    B. Wex and B. R. Kaafarani, J. Mater. Chem. C, 2017, 5, 8622
    DOI: 10.1039/C7TC02156A

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