Redshifting TADF Emission With a Bora‐Triptycene Lewis Acid

ABSTRACT

Binding of a Lewis acid to an emitter molecule is a versatile method to redshift the emission. This approach is underexplored for thermally activated delayed fluorescence (TADF) materials. In this study, we report that the addition of a Lewis acid can induce large (>100 nm) bathochromic shifts in the emission in sulfone‐based donor–acceptor TADF (DA‐TADF) emitters and for the first time in multi‐resonant TADF (MR‐TADF) emitters, whilst retaining TADF behaviour. This is achieved through the binding of a 9‐sulfonium‐10‐bora‐triptycene (BTripS) Lewis acid to the fluorophore carbonyl or sulfone moiety to form bench‐stable Lewis adducts. In contrast, when using B(C ₆ F ₅ ) ₃ as the Lewis acid, the generated adducts rapidly decompose on exposure to water to form H ₂ O‐B(C ₆ F ₅ ) ₃ . This work demonstrates that the formation of bench‐stable Lewis adducts has significant potential as a method to redshift the emission of two popular classes of TADF compounds. This provides a new approach to address the current challenge of accessing longer‐wavelength‐emitting MR‐TADF materials.