Effect of Molecular Aggregation on Photophysical Properties of Organoboron/Nitrogen- and Carbonyl/Nitrogen-Based Two Multi-Resonant Emitters

Abstract

Multi-resonant (MR) emitters exhibit intrinsic narrowband emission, yet they often suffer severe spectral broadening at high doping concentrations in films, which hinders their commercial application in high-color-purity organic light-emitting diodes (OLEDs). Such spectral broadening is generally caused by shoulder peak enhancement, a puzzling phenomenon in aggregation state. Two typical MR backbones, carbonyl/nitrogen-based DNK and organoboron/nitrogen-based DBN, which exhibit different spectral behaviors in films, were thus investigated and compared as an example. The experimental results indicate that DNKs exhibit noticeable shoulder peak enhancement at high concentrations in films, while DBNs maintain consistent spectra under the same conditions. The results of our molecular dynamics (MD) simulations reveal that in the aggregation state, DNK π–π stacking forms, thus introducing a new fluorescent component. The emission of DNK dimers is estimated to be located around the intrinsic MR shoulder peak, leading to a concentration-dependent shoulder peak enhancement in OLEDs. Conversely, no dimer-like aggregation states are observed for DBN in films due to the presence of bulky side groups, leading to its concentration-independent fluorescence spectra. This work combines MD simulation with high-level quantum chemistry (QC) calculation to establish an effective approach for understanding of the aggregation behavior of MR materials, and thus provides a deep insight into the spectral broadening by resolving the aggregation behaviors of MR emitters.

Keywords

molecular aggregation / multi-resonant emitter / photophysical properties

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