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

An easy-to-access, near UV-emitting linearly extended B,N-doped heptacene is designed and syn-thesized in good yields. This compound emits thermally activated delayed fluorescence at ambient temperature from a multi-resonant state and represents a rare example of a non-triangulene-based MR-TADF emitter. At lower temperatures triplet-triplet annihilation dominates. The compound sim-ultaneously possesses narrow, deep-blue emission with CIE coordinates of (0.17, 0.01). While de-layed fluorescence results mainly from triplet-triplet annihilation at lower temperatures in THF solu-tion, where aggregates form upon cooling, the TADF mechanism takes over around room tempera-tures 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 ∆EST using correlated wavefunction-based calculations. Based on these calculations, we predicted dramatically different optoelectronic behavior in terms of both ∆EST and the optical energy gap of two constitutional isomers where only the boron and nitrogen posi-tions change. A comprehensive structural, optoelectronic and theoretical investigation is presented. Further, the ability of the achiral molecule to assemble on a Au(111) surface to a highly ordered layer composed of enantiomorphic domains of racemic entities is demonstrated by scanning tunnel-ing microscopy.