Design of Efficient Exciplex Emitters by Decreasing the Energy Gap Between the Local Excited Triplet (3LE) State of the Acceptor and the Charge Transfer (CT) States of the Exciplex

Xiaofang Wei; Yanwei Liu; Taiping Hu; Zhiyi Li; Jianjun Liu; Ruifang Wang; Honglei Gao; Xiaoxiao Hu; Guanhao Liu; Pengfei Wang; Chun-Sing Lee; Ying Wang

doi:10.3389/fchem.2019.00188

Design of Efficient Exciplex Emitters by Decreasing the Energy Gap Between the Local Excited Triplet (³LE) State of the Acceptor and the Charge Transfer (CT) States of the Exciplex

Front Chem. 2019 Apr 9:7:188. doi: 10.3389/fchem.2019.00188. eCollection 2019.

Authors

Xiaofang Wei^{1

2}, Yanwei Liu^{2

3}, Taiping Hu^{2

3}, Zhiyi Li^{1

2}, Jianjun Liu^{1

2}, Ruifang Wang^{1

2}, Honglei Gao^{1

2}, Xiaoxiao Hu^{1

2}, Guanhao Liu^{1

2}, Pengfei Wang^{1

2}, Chun-Sing Lee⁴, Ying Wang^{1

2}

Affiliations

¹ Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China.
² School of Future Technology, University of Chinese Academy of Sciences, Beijing, China.
³ Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China.
⁴ Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong, Hong Kong.

Abstract

A series of thermally activated delayed fluorescence (TADF) exciplex based on the TX-TerPy were constructed. The electronic coupling between the triplet local excited states (³LE) of the donors and acceptor and the charge transfer states had a great influence on the triplet exciton harvesting and Φ_PL. Herein, based on this strategy, three donor molecules TAPC, TCTA, and m-MTDATA were selected. The local triplet excited state (³LE) of the three donors are 2.93, 2.72 and 2.52 eV in pure films. And the ³LE of TX-TerPy is 2.69 eV in polystyrene film. The energy gap between the singlet charge transfer (¹CT) states of TAPC:TX-TerPy (7:1), TCTA:TX-TerPy (7:1) and the ³LE of TX-TerPy are 0.30 eV and 0.20 eV. Finally, the Φ_PL of TAPC:TX-TerPy (7:1) and TCTA:TX-TerPy (7:1) are 65.2 and 69.6%. When we changed the doping concentration of the exciplex from 15% to 50%, the ratio of the triplet decreased, and Φ_PL decreased by half, perhaps due to the increased energy gap between ¹CT and ³LE. Therefore, optimizing the ¹CT, ³CT, and ³LE facilitated the efficient exciplex TADF molecules.

Keywords: energy gap; exciplex; organic light emitting diode (OLED); pure thermally activated delayed fluorescence (TADF); thixanthone (TX) derivatives.