A Deep Blue B,N-Doped Heptacene Emitter That Shows Both Thermally Activated Delayed Fluorescence and Delayed Fluorescence by Triplet-Triplet Annihilation.

An easy-to-access, near-UV-emitting linearly extended B,N-doped heptacene with high thermal stability is designed and synthesized in good yields. This compound exhibits thermally activated delayed fluorescence (TADF) at ambient temperature from a multiresonant (MR) state and represents a rare example of a non-triangulene-based MR-TADF emitter. At lower temperatures triplet-triplet annihilation dominates. The compound simultaneously possesses narrow, deep-blue emission with CIE coordinates of (0.17, 0.01). While delayed fluorescence results mainly from triplet-triplet annihilation at lower temperatures in THF solution, where aggregates form upon cooling, the TADF mechanism takes over around room temperature in solution when the aggregates dissolve or when the compound is well dispersed in a solid matrix. The potential of our molecular design to trigger TADF in larger acenes is demonstrated through the accurate prediction of Δ