Beschreibung:
<jats:p>Three novel donor-acceptor molecules comprising the underexplored pyridazine (Pydz) acceptor moiety have been synthesized and their structural, electrochemical and photophysical properties thoroughly characterized. Combining Pydz with two phenoxazine donor units linked via a phenyl bridge in a <jats:italic>meta</jats:italic> configuration (<jats:bold>dPXZMePydz</jats:bold>) leads to high reverse intersystem crossing rate <jats:italic>k</jats:italic><jats:sub>RISC</jats:sub> = 3.9 · 10<jats:sup>6</jats:sup> s<jats:sup>−1</jats:sup> and fast thermally activated delayed fluorescence (TADF) with &lt;500 ns delayed emission lifetime. Efficient triplet harvesting via the TADF mechanism is demonstrated in OLEDs using <jats:bold>dPXZMePydz</jats:bold> as the emitter but does not occur for compounds bearing weaker donor units.</jats:p>