To design ultrabright fluorescence AIEgens in the solid state, a new crystal engineering strategy that enables monomeric emission by preventing intermolecular electronic interactions and excimer formation is required. Optimization of the quantum yields, emission colors, crystallinities, and molecular orientations of solid-state fluorescent dyes is required for advanced OLEDs. In this lecture, I would like to talk about two case studies. First, we discuss solid-state luminescence with 9,10-bis(dialkylamino)anthracene (BDAA) derivatives. BDAAs show monomeric emission. The fluorescence of BDAAs were monomeric, probably due to their large Stokes shifts with minimal structural relaxations, which can cause so-called exciton self-trapping, a process where local lattice deformations trap excitons into a single luminophore. Second, we report the unique crystallinity and luminescence properties of bridged-stilbene with monomeric emission. We introduced propylene moieties to distyrylbenzene (DSB) as bridges between the phenyl rings either side of its C=C bonds. The bridged DSB derivatives formed compact crystals that emit colors similar to those of the same molecules in dilute solution, with high quantum yields. The introduction of flexible seven-membered rings to the DSB core produced moderate distortion and steric hindrance in the DSB π-plane.
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