An extended π-backbone for highly efficient near-infrared thermally activated delayed fluorescence with enhanced horizontal molecular orientation

Abstract

Near-infrared thermally activated delayed fluorescence (NIR-TADF) materials with emission over 700 nm have been insufficiently investigated mainly due to the limited choice of strong donor/acceptor units for molecular construction and the limited electronic coupling between the donors and acceptors. Herein, a novel D–A1–A2–A3 configuration was developed for the design of a NIR-TADF material (TPA-CN-N4-2PY), in which three types of sub-acceptor units (CN: cyano; N4: dipyrido[3,2-a:2′,3′-c]phenazine; PY: pyridine) were incorporated into a molecular skeleton to reinforce the electron-accepting strength. The attachment of two pyridine units on TPA-CN-N4 produced TPA-CN-N4-2PY with an extended π-backbone, which shifted the electroluminescence (EL) emission into the NIR region and enhanced the horizontal ratio of emitting dipole orientation (Θ//) simultaneously. TPA-CN-N4-2PY-based OLEDs demonstrated a record-high external quantum efficiency (EQE) of 21.9% with an emission peak at 712 nm and Θ// = 85% at the doping ratio of 9.0 wt%. On the contrary, the parent compound TPA-CN-N4-based OLEDs at the same doping ratio achieved an EQE of 23.4% at 678 nm with Θ// = 75%. This multiple sub-acceptors approach could enrich the design strategy of the NIR-TADF materials, and the large conjugated system could improve the Θ// for achieving efficient emitters.

Graphical abstract: An extended π-backbone for highly efficient near-infrared thermally activated delayed fluorescence with enhanced horizontal molecular orientation

Supplementary files

Article information

Article type
Communication
Submitted
09 Oct 2021
Accepted
22 Nov 2021
First published
29 Nov 2021

Mater. Horiz., 2022, Advance Article

An extended π-backbone for highly efficient near-infrared thermally activated delayed fluorescence with enhanced horizontal molecular orientation

J. He, Y. Tang, K. Zhang, Y. Zhao, Y. Lin, C. Hsu, C. Chen, T. Chiu, J. Lee, C. Wang, C. Wu and J. Fan, Mater. Horiz., 2022, Advance Article , DOI: 10.1039/D1MH01651B

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