Fan-Shaped ExtendingConjugation Strategies for AchievingNarrowband Emissions of Boron–Nitrogen-Based Molecules

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials have attracted extensive attention due to their 100% exciton utilization efficiency and narrowband emissions. Numerous tube-shaped MR-TADF emitters with full-color narrowband emissions have been reported, and updated molecular design strategies need to be proposed to find more molecular “recipes” to narrow the emission spectral range. Upon changing the shape of the fluorophore from a tubular to fan-shaped structure, the investigated molecules exhibit narrowband emissions based on the analysis of the geometric and electronic structures, reorganization energies, charge transfer characters upon excitation, and absorption and emission properties. The small reorganization energies and short-range charge transfer properties upon excitation are the key to narrowing the spectral range of the molecules. Such theoretical investigations give an in-depth insight into the structure–property relationship, and the updated molecular design strategies would provide important guidance for the design of multiple-resonance molecules with narrowband emissions.