2, Academia Sinica, Taipei, , Taiwan
Organic molecules with efficient thermally activated delayed fluorescence (TADF) are emerging as attractive emitters in OLEDs because of the achievable 100% internal quantum efficiency. In this talk, by subtle manipulations of intramolecular charge transfer, our recent works on acridine-based TADF materials will be presented. One of this series TADF materials exhibits nearly 100% photoluminescence quantum yield, excellent thermal stability, and a horizontal dipole ratio of 83%, leading to extremely efficient blue organic EL with external quantum efficiency (EQE) of ~37%. In addition, efficient and tunable blue-green to yellow TADF emitters capable of generating OLED EQEs of > 31% were developed adopting acridine as donor unit and CN-substituted benzene, pyridine and pyrimidine as acceptor units will also be reported. These materials permit one to systematically probe the influence of different acceptor strengths and also the influence of tunable conformations (twist angles) within the acceptor moieties through controlling the orientation of asymmetric heteroaromatic ring relative to the donor component. TADF can also be achieved by exciplex formed through intermolecular charge transfer between a hole-transporting material (HTM) and an electron-transporting material (ETM). Some efficient OLEDs based on exciplex system will be presented. In addition, for the first time, the characterization of exciplex structure with transient IR will also be presented.