Red thermally activated delayed fluorescence emitters based on phenazine-derived electron donors and solution-processed OLEDs

Despite recent advancements in red thermally activated delayed fluorescence (TADF) emitters, most reported red TADF emitters feature rigid acceptor units, which make them insoluble and unsuitable for solution-processed organic light-emitting diodes (OLEDs). To tackle this issue, two new TADF emitters, 2tBuInPz-BP33 and 2tBulnPz-XO33, have been designed by connecting a novel phenazine-based electron-donor to the derivative of benzophenone acceptor. The highly twisted donor-acceptor structure, along with an appropriate distribution of the highest occupied molecular orbital/lowest unoccupied molecular orbital, has resulted in a very small singlettriplet energy gap. Additionally, the peripheral tert-butyl-modified multi-ring phenazine donor unit increases the molecular solubility and enhances the electron-donating ability of donors. Finally, solution-processed OLEDs based on 2tBulnPz-XO33 exhibit a red emission peak at 626 nm and low efficiency roll-off, achieving an external quantum efficiency of 6.9%.