Integrating the Emitter and Host Characteristics of Donor-Acceptor Systems through Edge-Spiro Effect Toward 100% Exciton Harvesting in Blue and White Fluorescence Diodes

Herein, by utilizing edge-spiro effect to modulate intramolecular charge transfer and intermolecular interactions, emitter and host characteristic are integrated in simple donor-acceptor systems named SFInxTz. As emitter, SFI34pTz realizes true-blue thermally activated delayed fluorescent (TADF) diodes with an external quantum efficiency (EQE) of 25.3% and Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.20). As host, it can endow the yellow devices with the maximum EQE about 18%. When SFI34pTz serves as both blue emitter and yellow host material in pure fluorescence white device, the maximum efficiencies are as high as 22.9% for EQE and 52.4 lm W-1 for power efficiency, and stable electroluminescence spectra are successfully realized with CIE coordinates of (0.32 +/- 0.01, 0.42 +/- 0.02). Above all, SFI34pTz manifests the effectiveness of the edge-spiro strategy in developing host-featured blue TADF dyes for high-performance blue devices and white organic light-emitting diodes (WOLEDs). More importantly, a novel blue-orange-blue sandwich device structure consisting of all-TADF materials for high-efficiency pure fluorescence WOLEDs is proposed.