Full-Color Delayed Fluorescence Materials Based on Wedge-Shaped Phthalonitriles and Dicyanopyrazines: Systematic Design, Tunable Photophysical Properties, and OLED Performance

Purely organic light-emitting materials, which can harvest both singlet and triplet excited states to offer high electron-to-photon conversion efficiencies, are essential for the realization of high-performance organic light-emitting diodes (OLEDs) without using precious metal elements. Donor-acceptor architectures with an intramolecular charge-transfer excited state have been proved to be a promising system for achieving these requirements through a mechanism of thermally activated delayed fluorescence (TADF). Here, luminescent wedge-shaped molecules, which comprise a central phthalonitrile or 2,3-dicyanopyrazine acceptor core coupled with various donor units, are reported as TADF emitters. This set of materials allows systematic fine-tuning of the band gap and exhibits TADF emissions that cover the entire visible range from blue to red. Full-color TADF-OLEDs with high maximum external electroluminescence quantum efficiencies of up to 18.9% have been demonstrated by using these phthalonitrile and 2,3-dicyanopyrazine-based TADF emitters.