Highly Efficient Thermally Activated Delayed Fluorescence from an Excited-State Intramolecular Proton Transfer System

Thermally
activated delayed fluorescence (TADF) materials have
shown great potential for highly efficient organic light-emitting
diodes (OLEDs). While the current molecular design of TADF materials
primarily focuses on combining donor and acceptor units, we present
a novel system based on the use of excited-state intramolecular proton
transfer (ESIPT) to achieve efficient TADF without relying on the
well-established donor–acceptor scheme. In an appropriately
designed acridone-based compound with intramolecular hydrogen bonding,
ESIPT leads to separation of the highest occupied and lowest unoccupied
molecular orbitals, resulting in TADF emission with a photoluminescence
quantum yield of nearly 60%. High external electroluminescence quantum
efficiencies of up to 14% in OLEDs using this emitter prove that efficient
triplet harvesting is possible with ESIPT-based TADF materials. This
work will expand and accelerate the development of a wide variety
of TADF materials for high performance OLEDs.