Deep-blue luminescent compound that emits efficiently both in solution and solid state with considerable blue-shift upon aggregation

Abstract

We have designed and synthesized a novel deep-blue luminescent compound (WuFDA), which can emit efficiently both in solution and in the aggregated state; the fluorescence emission maximum of WuFDA in the aggregated state shows a remarkable blue-shift from that shown in the dilute solution. Moreover, WuFDA shows interesting fluorescent behaviour in mixed solvent systems of THF–H₂O, and a solvent effect in different polar solvents. These unusual phenomena have been interpreted by studies of the single crystalline structure of WuFDA and density functional theory (DFT) investigations. The special chemical structure (containing a planar conjugated fluorene core and strong polar groups (–NH and –F)) and their location in the molecule formed a typical non-planar D–π–A molecule with strong internal charge transfer (ICT). Such a polar molecule possesses the ability to form hydrogen bond interactions with itself, as well as with the polar solvents. Both the ICT effect and the intermolecular hydrogen bond interactions play very important roles in the geometrical manner of aggregation and the fluorescent behaviours of the WuFDA. In addition, WuFDA exhibited good thermal stability, with 5% and 10% weight-loss temperatures (T_d) of WuFDA in nitrogen of 399 and 414 °C, respectively, and the glass transition temperature (T_g) was about 161 °C.