Intermolecular hydrogen bonds induce highly emissive excimers: Enhancement of solid-state luminescence

Aggregation induced emission (AIE) is an amazing property for light emitting materials and has attracted much attention. Here, we report a new kind of AIE materials: fluorenone derivates 2,7-dip-tolyl-fluorenone (DTFO) and 2,7-bis(4-(tert-butylthio)phenyl)-fluorenone (DSFO). Strong light emissions with a large Stokes shift and long lifetime in the solid state originate from the formation of excimers. The crystal structure of DSFO shows that every two molecules are bound together even in the ground state by intermolecular hydrogen bonds and form a particular dimer. When this dimer is excited, it turns into an excimer without arrangement adjustment and likewise without repulsive interactions when the excimer decays back to the dimer; so, the nonradiative decay pathways that exist in common excimers are greatly reduced and thus induce a strongly enhanced luminescence in the solid state. OLED devices employing DTFO as light emitting layers are fabricated and evaluated.