Rational Molecular Design Strategy for Host Materials in Thermally Activated Delayed Fluorescence-OLEDs Suitable for Solution Processing

Herein,a novel core molecule for V-shaped host moleculeswas synthesized,wherein two carbazoles were directly linked to cyclohexane. Cy-mCP and Cy-mCBP hosts were also successfullyprepared for solution-processable thermally activated delayed fluorescenceorganic light-emitting diodes (TADF-OLEDs). The Cy-mCP and Cy-mCBP molecules contained a cyclohexane linkerdirectly linked to two small molecular hosts (mCP and mCBP), exhibitingtwice the molecular weight while maintaining the basic propertiesof a single host molecule with improved film-forming ability and solubilityin organic solvents. These host materials showed superior thermalstability and high glass transition temperatures compared to lowermolecular weight hosts. Green TADF-OLEDs were prepared usingthe two host materials and 2,4,5,6-tetra-(3,6-di-tert-butylcarbazol-9-yl)-1,3-dicyanobenzene (t4CzIPN) emitter, achievingdevice efficiencies similar to that of a low-molecular-weight host.However, after the incorporation of a V-shaped host, superior characteristicswere observed in terms of the thermal stability and operational stabilityof the device. The synthesis of V-shaped molecules by directly linkingtwo carbazoles to a cyclohexane linker is promising for the developmentof different hosts for solution-processable OLEDs.