Hydroxy‐Tetraphenylimidazole Derivatives as Efficient Blue Emissive Materials for Electroluminescent Devices.

Herein, three hydroxy‐tetraphenylimidazole (HPI)‐based fluorophores (HPI‐TPA, HPI‐PCz, and HPI‐CzP) are designed and synthesized by disubstituted HPI core with arylamine units of triphenylamine (TPA), phenyl carbazole (PCz), and carbazole phenyl (CzP) at 3,5‐positions of the N‐phenyl ring of HPI, respectively. Their photophysical properties are theoretically and experimentally examined. HPI‐TPA shows a hybridized local and charge transfer (HLCT) excited state characteristic and emits deep blue color via an HLCT mechanism, while both HPI‐PCz and HPI‐CzP exhibit excited‐state intramolecular proton transfer (ESIPT) property and display pure keto form emissions. They possess high thermal stability and are successfully fabricated as emitters in organic light‐emitting diodes (OLEDs). All devices exhibit intense blue color emissions with low turn‐on voltages (3.5–3.7 V). Particularly, HPI‐TPA‐based OLED emits light in the deep‐blue region with a high maximum external quantum efficiency (EQEmax) of 3.77% and a decent efficiency roll‐off. [ABSTRACT FROM AUTHOR]