Redshifting TADF Emission With a Bora-Triptycene Lewis Acid.

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(C6F5)3 as the Lewis acid, the generated adducts rapidly decompose on exposure to water to form H2O-B(C6F5)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.