Highly Efficient Blue Thermally Activated Delayed Fluorescence Emitters with a Triphenylamine-Based Macrocyclic Donor
Journal
ADVANCED OPTICAL MATERIALS
Journal Volume
11
Journal Issue
5
Date Issued
2023
Author(s)
Abstract
This work reports the incorporation of a triphenylamine-based macrocyclic donor to design new donor-π-acceptor-configured blue thermally activated delayed fluorescence (TADF) emitters. The X-ray structure analyses manifest the degree of twisted conformations that can be modulated by methyl substituents of the π-bridge and macrocyclic donor, leading to well-separated highest occupied natural transition orbital and lowest unoccupied natural transition orbital frontier orbitals, thus sufficiently small singlet–triplet energy difference (ΔEST) for TADF. The theoretical analyses elucidate the structure–property relationship and reveal the beneficial effect of macrocyclic donor on increasing reverse intersystem crossing (RISC) process that can contribute to improved triplet-upconversion efficiency. The blue device employing c-NN-TRZ as emitter gave a maximum external quantum efficiecny (EQEmax) of 26.3% as compared to that (19.1%) of the device using the model compound DPA-MeTRZ without the macrocyclic donor, suggesting the contribution of macrocyclic donor to enhance device performance. Benefiting from the combined advantages of macrocyclic donor and methyl substituents, the device incorporating c-NN-MeTRZ as emitter achieves an outstanding EQEmax of 32.2%, which is attributed to the more horizontally oriented emission dipoles as well as the significantly accelerated RISC rate constant (kRISC) resulting from reduced ΔEST. This work represents a new strategy of designing twisted TADF emitter incorporating macrocyclic donor to achieve highly efficient blue device.
Subjects
horizontal dipole ratio; macrocyclic donor; thermally activated delayed fluorescence emitter; triphenylamine; twisted conformation; LIGHT-EMITTING DIODE; SPACE CHARGE-TRANSFER; DESIGN; MOLECULES; STRATEGY; SINGLET
SDGs
Publisher
WILEY-V C H VERLAG GMBH
Type
journal article