Solid‐State Fluorophores with Combined Excited‐State Intramolecular Proton Transfer‐Aggregation‐Induced Emission as Efficient Emitters for Electroluminescent Devices

Abstract

A series of excited‐state intramolecular proton transfer (ESIPT)–aggregate‐induced emission (AIE) solid‐state fluorophores (TTHPI, PTHPI, and ATHPI) are reported as self‐absorption‐free emitters for electroluminescent (EL) devices. The molecules contain 2‐(2‐hydroxyphenyl)‐1,4,5‐triphenylimidazole as an ESIPT core being double functionalized with AIE‐active luminogen of tetraphenylethene and hole‐transporting moiety (triphenylamine, N‐(4‐phenyl)phenoxazine, or N‐(4‐phenyl)‐9,9‐dimethylacridine) to improve their solid‐state emission due to the AIE effect and hole‐transporting capability. The ESIPT, AIE, and photophysical properties are theoretically and experimentally studied. All molecules demonstrate ESIPT and AIE characters with intense sky‐blue/green color emissions from a pure keto‐form emission in the solid‐state and photoluminescence quantum yields of 41–74%. These ESIPT–AIE fluorophores exhibit high thermal and electrochemical stabilities with decent hole mobilities and are successfully utilized as emitters in organic light‐emitting diodes (OLEDs). All devices show pure keto‐form EL emissions with moderate‐to‐good EL performances. Particularly, the TTHPI‐based device achieves excellent EL performance with a maximum external quantum efficiency (EQEmax) of 5.21%, a maximum current efficiency (CEmax) of 11.17 cd A−1, and a slight efficiency roll‐off.