Rational molecular design of deep blue thermally activated delayed fluorescent emitters for high efficiency fluorescent and hyperfluorescent devices

Two deep blue thermally activated delayed fluorescent (TADF) emitters with peripheral alkyl branches surrounding the donor and acceptor moieties were synthesized to explore ideal design of deep blue TADF emitters for fluorescence and hyperfluorescence in terms of quantum efficiency. The TADF emitters having the multiple alkyl branches protecting the donor and acceptor moieties performed better than the emitter without the alkyl branch or with the alkyl branch only in the donor or acceptor unit. The TADF emitters with the peripheral alkyl branches both in the donor and acceptor units showed a high quantum efficiency above 22.0%, a deep blue color coordinate of (0.15, 0.20), and doping concentration independent emission color as TADF emitters, and 13.7% quantum efficiency in the TADF sensitized hyperfluorescent device. Therefore, the multiple alkyl modification method of both donor and acceptor units of TADF emitters can resolve the issues of TADF emitters for ideal device performances.