Incorporating Thermally Activated Delayed Fluorescence into Mechanochromic Luminescent Emitters: High‐Performance Solution‐Processed Yellow Organic Light Emitting Diodes

Abstract Multifunctional materials with stimuli‐responsive features are demonstrated to be promising smart materials. In this work, three multifunctional materials, namely 5TzPmPXZ, 7TzPmPXZ, and 5,7TzPmPXZ, are constructed by integrating phenoxazine with electron‐acceptor core [1,2,4]triazolo[1,5‐a]pyrimidine (TzPm). Intriguingly, these materials exhibit not only thermally activated delayed fluorescence but also multicolor luminescence switching which is caused by the phase transitions between microcrystalline and amorphous states upon external stimuli. Moreover, the solution‐processed organic light emitting diodes (OLEDs) fabricated with these materials furnish a high external quantum efficiency up to 14.3% and the Commission Internationale de l'Eclairage coordinates of (0.43, 0.53), which represents the state‐of‐the‐art performance for solution‐processed yellow OLEDs.