Highly Efficient Blue Thermally Activated Delayed Fluorescence Emitters with a Triphenylamine-Based Macrocyclic Donor

This work reports the incorporation of a triphenylamine-based macrocyclic donor to design new donor-pi-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 pi-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 (Delta E-ST) 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 (EQE(max)) 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 EQE(max) of 32.2%, which is attributed to the more horizontally oriented emission dipoles as well as the significantly accelerated RISC rate constant (k(RISC)) resulting from reduced Delta E-ST. This work represents a new strategy of designing twisted TADF emitter incorporating macrocyclic donor to achieve highly efficient blue device.t blue organic light-emitting diodes.

Automated summary

This work presents the design of new blue TADF emitters with a triphenylamine-based macrocyclic donor, which is found to enhance reverse intersystem crossing and triplet-upconversion efficiency. Experimental results show that incorporating the macrocyclic donor in the blue device significantly improves its performance, achieving a maximum external quantum efficiency of 32.2%. This study offers a new strategy for designing efficient blue organic light-emitting diodes.