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. 2023 May 11;13(1):7644.
doi: 10.1038/s41598-023-34623-9.

Multiple donor-acceptor design for highly luminescent and stable thermally activated delayed fluorescence emitters

Bhagya Madushani  1 , Masashi Mamada  2   3 , Kenichi Goushi  1 , Thanh Ba Nguyen  1 , Hajime Nakanotani  1 , Hironori Kaji  4 , Chihaya Adachi  5   6
Affiliations

Multiple donor-acceptor design for highly luminescent and stable thermally activated delayed fluorescence emitters

Bhagya Madushani et al. Sci Rep. .

Abstract

A considerable variety of donor-acceptor (D-A) combinations offers the potential for realizing highly efficient thermally activated delayed fluorescence (TADF) materials. Multiple D-A type compounds are one of the promising families of TADF materials in terms of stability as well as efficiencies. However, those emitters are always composed of carbazole-based donors despite a wide choice of moieties used in linearly linked single D-A molecules. Herein, we developed a multiple D-A type TADF compound with two distinct donor units of 9,10-dihydro-9,9-dimethylacridine (DMAC) and carbazole as the hetero-donor design. The new emitter exhibits high photoluminescence quantum yield (PLQY) in various conditions including polar media blend and high concentrations. Organic light-emitting diodes (OLEDs) showed a reasonably high external quantum efficiency (EQE). In addition, we revealed that the multiple-D-A type molecules showed better photostability than the single D-A type molecules, while the operational stability in OLEDs involves dominant other factors.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Absorption and fluorescence spectra at room temperature, and phosphorescence spectrum at 77 K for 2Cz2DMAC2BN in toluene. Inset: Chemical structures of 2Cz2DMAC2BN. (b) PL spectra for 2Cz2DMAC2BN doped films of mCBP and neat 2Cz2DMAC2BN film. (c) Temperature dependence of transient PL decay for 6-wt%-2Cz2DMAC2BN doped film of mCBP.
Figure 2
Figure 2
OLED performances for 2Cz2DMAC2BN-based devices. (a–c) The devices with mCBP host. (d–f) The devices with CCP host. (g–i) The devices with PPT host. (a,d,g) Current density–voltage characteristics. (b,e,h) EQE-luminance characteristics. (c,f,i) EL spectra in the OLEDs at 6 V.
Figure 3
Figure 3
(a) Chemical structures of TADF materials under investigation. (b) Photostability of TADF materials in the neat films. PL intensity change versus excitation time irradiated by continuous-wave laser light at 355 nm (excitation power of 2.5 W cm−2). Inset: PL spectra for the neat films. (c) Device operational stability for the OLED having EML of 15 wt%-TADF doped mCBP. Luminance change versus operational time at an initial luminance of 100 cd m−2. Inset: EL spectra for the devices.
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