Reversible Crystal‐to‐Crystal Phase Transitions with High‐Contrast Luminescent Alterations for a Thermally Activated Delayed Fluorescence Emitter
Hanbo Yu, Xiaoxian Song, Ning Xie, Jiaxuan Wang, Chenglong Li, Yue Wang
Abstract
Abstract Merging thermally activated delayed fluorescence (TADF) and mechanochromic luminescence (MCL) into one single molecule is a promising strategy for developing multifunctional organic materials. Herein, a unique multifunctional molecule TPA‐DQP, comprising a large π‐conjugated diquinoxalino[2,3‐ a :2′,3′‐ c ]phenazine (DQP) as the acceptor and triphenylamine (TPA) as the donor, is designed and synthesized. TPA‐DQP possesses polymorphism, efficient TADF emission as well as MCL property with high‐contrast in emission colors from 576 to 706 nm. Reversible crystal‐to‐crystal phase transitions in response to external stimuli such as vapor fuming and heating are realized on the basis of the two polymorphs of TPA‐DQP. The distinct crystal‐to‐crystal phase transition is attributed ultimately to the change of packing arrangements and intermolecular interactions of the two polymorphs under stimuli. Furthermore, TPA‐DQP‐based organic light emitting diode (OLED) device achieves external quantum efficiency as high as 18.3% at 676 nm, which represents the best performance for deep‐red OLEDs based on MCL‐active TADF emitters. This study reports a novel MCL‐active TADF material that exhibits crystal‐to‐crystal phase transition and brings insight into the underlying relationship between molecular packing modes and the photoluminescent behavior.