Boron- and nitrogen-embedded blue multi-resonance emitters with low triplet energy

B,N-doped multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters are of significant interest for realizing the high efficiency and remarkable color purity of optoelectronic devices. Due to their moderate singlet-triplet energy gap, managing triplet state (T-1) energy is important to enhance the performance of these devices. Herein, polycyclic aromatic hydrocarbons (PAHs), such as pyrene and anthracene, are appended to the t-DABNA structure, resulting in t-DABNA-PAH compounds, namely t-DABNA-pyr and t-DABNA-ant. Both compounds display sky-blue fluorescence which lacks TADF characteristics while preserving high photoluminescence quantum yield (PLQY) and high color purity. The compounds possess low T-1 energy (similar to 2.0 eV), which is advantageous for suppressing the accumulation of undesirable long-lived T-1 excitons. Particularly, t-DABNA-pyr exhibits emissions with a narrow full width at half maximum (similar to 33 nm) and a high PLQY (similar to 100%) in both solution and rigid states. Theoretical studies further suggest that the low-energy T-1 state is localized at the PAH moiety.