Multifunctional emitters with TADF, AIE, polymorphism and high-contrast multicolor mechanochromism: Efficient organic light-emitting diodes

Organic multifunctional luminescent materials have drawn growing attention due to their diverse emissive mechanism and potential application in luminescent field. Herein, a series of cyanobenzene-decorated dimethylacridine-quinoline conjugates is designed and synthesized, which exhibit thermally activated delayed fluorescence (TADF), aggregation-induced emission (AIE), polymorphism and multicolor mechanochromic luminescence (MCL) with high contrast beyond 75 nm. Significantly, structure-property investigations via the in-depth analysis of molecular conformations and three-dimensional supramolecular framework of the polymorphic crystals demonstrate that the diverse conformations and abundant noncovalent interactions have a predominant impact on aggregation-dependent TADF property and emission wavelength. The quasi-equatorial conformational electron-donating unit and quasi-planar structural electron-withdrawing segment in aggregation states of the emitter are beneficial for accelerating the rate of the reverse intersystem crossing, enhancing TADF character, and promoting the emission with a bathochromic shift. The organic light-emitting diodes (OLEDs) employing these emitters achieve good device performance with an external quantum efficiency (EQE) of 14.6%.