AbstractAn approach to the design of nido‐carborane‐based luminescent compounds that can exhibit thermally activated delayed fluorescence (TADF) is proposed. 7,8‐Dicarba‐nido‐undecaboranes (nido‐carboranes) having various 8‐R groups (R=H, Me, i‐Pr, Ph) are appended to the meta or para position of the phenyl ring of the dimesitylphenylborane (PhBMes2) acceptor, forming donor–acceptor compounds (nido‐m1–m4 and nido‐p1–p4). The bulky 8‐R group and meta substitution of the nido‐carborane are essential to attain a highly twisted arrangement between the donor and acceptor moieties, leading to a very small energy splitting between the singlet and triplet excited states (ΔEST <0.05 eV for nido‐m2, ‐m3, and ‐p3). These compounds exhibit efficient TADF with microsecond‐range lifetimes. In particular, nido‐m2 and ‐m3 display aggregation‐induced emission (AIE) with TADF properties.