Modulating the Excited States of Thermally Activated Delayed Fluorescence Conjugated Polymers by Introducing Hydrogen Bonding into the Acceptor for High-Performance OLEDs

Constructing high-performance thermally activated delayed fluorescence (TADF)-conjugated polymers for solution-processed OLEDs is still challenging. Rationally tuning the acceptors has been proven to be an effective way. Therefore, we incorporate pyridine and pyrimidine into the acceptor of conjugated TADF polymers to not only adjust the electron-withdrawing ability of acceptors but also induce the intramolecular hydrogen bonds. Moreover, the excited states of the new synthesized polymers, p-PXZ-XN-Py and p-PXZ-XN-Pm, are also optimized due to the modulated acceptor. Both polymers show the enhanced spin orbital coupling effect and thereby high reverse intersystem crossing rates. Additionally, the construction of intramolecular hydrogen bonds in the acceptors significantly restricts molecular relaxation and thus reduces the nonradiative transition rates of both polymers. Consequently, the EQE(max) values of p-PXZ-XN-Py and p-PXZ-XN-Pm based OLEDs are promoted to 20.5% at 568 nm and 20.4% at 572 nm, respectively, which rank the first tier among the reported TADF-conjugated polymers with wavelength over 560 nm. Furthermore, they simultaneously maintain a low turn-on voltage of 2.9 V, a low efficiency roll-off of about 12.0% at 500 cd m(-2), and a high brightness approaching 10,000 cd m(-2). Therefore, this work provides a new perspective of acceptor modulation for the construction of high-performance TADF-conjugated polymers.