Modulating intermolecular interactions and high-order triplet states of anthracene host materials for efficient TTA-UC with a Naphtho[2,3-d][1,3,2]diazaborole scaffold and its N-substituents.

Three naphtho[2,3-d][1,3,2]diazaborole (NDB)-functionalized anthracene host materials (Ph-NDB, Np-NDB, and DBF-NDB) were designed and synthesized. The NDB skeleton and variable N-atom substituents synergistically modulate intermolecular interactions and higher-order triplet energy levels. Theoretical and photophysical investigations reveal that the S1 and T1 states of the three compounds are localized on the anthracene core, while the T2 state is dominated by the NDB skeleton. The T3 state exhibits distinct substituent-dependent characteristics: in Np-NDB, it is exclusively governed by naphthyl groups on N-atoms, whereas in Ph-NDB and DBF-NDB, it is co-regulated by the anthracene core and phenyl groups on N-atoms. As a result, Np-NDB exhibits stronger TTA-UC capabilities than the reference sample DPA and other compounds. The three compounds possess bipolar charge transport properties and excellent thermal stability, with melting temperatures above 300 °C. An Np-NDB-based blue OLED achieves a maximum EQE of 8.00%, surpassing the commercial anthracene-based host BH (7.55%). This work clarifies the unique modulation mechanism of NDB skeletons and N-substituents toward high-order triplet states and intermolecular interactions, providing a feasible molecular design strategy for developing high-efficiency TTA-UC host materials for blue OLEDs.