OBO-Fused Benzo[fg]tetracene as Acceptor With Potential for Thermally Activated Delayed Fluorescence Emitters.

Zhen Zhang,Eli Zysman-Colman,Martin Nieger,Shiv Kumar,Stefan Bräse,Zahid Hassan,Fabian Hundemer,Anna Köhler,Sergey Bagnich,Eduard Spuling

doi:10.3389/fchem.2020.563411

Abstract

Six luminophores bearing an OBO-fused benzo[fg]tetracene core as an electron acceptor were designed and synthesized. The molecular structures of three molecules (PXZ-OBO, 5PXZ-OBO, 5DMAC-OBO) were determined by single crystal X-ray diffraction studies and revealed significant torsion between the donor moieties and the OBO acceptor with dihedral angles between 75.5 and 86.2°. Photophysical studies demonstrate that blue and deep blue emission can be realized with photoluminescence maxima (λPL) ranging from 415 to 480 nm in mCP films. The emission energy is modulated by simply varying the strength of the donor heterocycle, the number of donors, and their position relative to the acceptor. Although the DMAC derivatives show negligible delayed emission because of their large singlet-triplet excited state energy difference, ΔEST, PXZ-based molecules, especially PXZ-OBO with an experimental ΔEST of 0.25 eV, demonstrate delayed emission in blend mCP films at room temperature, which suggests triplet exciton harvesting occurs in these samples, potentially by thermally activated delayed fluorescence.

Highlights

As one of the most promising electroluminescent technologies, organic light-emitting diodes (OLEDs) have attracted significant attention and are being commercialized across a number of different product lines (Endo et al, 2011; Uoyama et al, 2012; Tao et al, 2014; Wong and Zysman-Colman, 2017; Yang et al, 2017)
We systematically investigate the impact of the number, identity of the donor (9,9-dimethyl-9,10-dihydroacridine, DMAC, and 10H-phenoxazine, PXZ), and their position relative to OBO-based benzo[fg]tetracene acceptor (OBO) on the optoelectronic properties of the emitter (Figure 1)
These six OBO-based derivatives were successfully synthesized via a three-step procedure (Scheme 1)

Summary

INTRODUCTION

As one of the most promising electroluminescent technologies, organic light-emitting diodes (OLEDs) have attracted significant attention and are being commercialized across a number of different product lines (Endo et al, 2011; Uoyama et al, 2012; Tao et al, 2014; Wong and Zysman-Colman, 2017; Yang et al, 2017). TADF emitters rely mainly on a twisted donor acceptor structure (Chen et al, 2016; Wang et al, 2017). Suzuki and coworkers (Suzuki et al, 2015) synthesized two stable boron-containing compounds based on the bis(mesityl)borane (BMes2) acceptor and realized efficient sky-blue [Commission Internationale de l’Eclairage (CIE): 0.18, 0.43] and green (CIE: 0.22, 0.55) TADF OLEDs with maximum external quantum efficiency (EQEmax) of 21.6% (2DAC-Mes3B) and 22.8% (PXZ-Mes3B), respectively. The boronate ester–based device exhibited only the EQEmax of 5.2% because of its low PLQY of 28%, its bluer emission at 471 nm (CIE: 0.17, 0.22) revealed the potential of the boronate ester acceptor for blue and even deep blue TADF emitters. We systematically investigate the impact of the number, identity of the donor (9,9-dimethyl-9,10-dihydroacridine, DMAC, and 10H-phenoxazine, PXZ), and their position relative to OBO on the optoelectronic properties of the emitter (Figure 1)

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT