Investigation On The Synthesis And Photophysical Properties Of A Novel Class Of Solid-state Blue-emitting P-Quaterphenyls Laterally Substituted With A Dimesitylboryl Group

The organic light emitting diodes (OLEDs) employing organic fluorophores as emitters have attracted considerable interest because of their potential applications in flat panel displays and solid-state lighting etc. In OLEDs, organic emitters are used as thin films and thus the external quantum efficiency of the devices is greatly dependent on the fluorescence quantum yield of the emissive materials in the solid state. However, most organic fluorophores are highly emissive only in the dilute solution and tend to show a decrease of fluorescence efficiency in the solid state due to the severe fluorescence quenching, which may result from the intermolecular electronic interactions such as aggregate or excimer formation and energy migration in the solid state. And thus it is still challenging to design and synthesize organic emissive materials with excellent solid state quantum yield, especially blue emissive materials.In the context, a new family of para-quarterphenyls1-6laterally substituted with a bulky electron-accepting dimesitylboryl group have been designed and synthesized. These compounds were characterized by X-ray crystallography, UV-vis and fluorescence spectroscopy, DFT calculations as well as thermogravimetric analysis (TGA), differential scanning clorimetry (DSC) and cyclic voltammetry (CV). X-ray single crystal analysis revealed that the para-quarterphenyl main chain framework exhibits a twisted structure due to the steric effect of the lateral boryl group, and the intermolecular interactions are effectively suppressed in the solid state. Despite the significantly twisted main-chain structure, these molecules still display efficient intramolecular charge-transfer emissions with large Stokes shifts. An intriguing finding is that all these molecules show bright fluorescence with good to excellent quantum yield in the blue region in the solid state (ΦF=0.60-0.99). In addition, the two representative para-quarterphenyls3and4containing both the electron-accepting boryl group and the electron-donating carbarzolyl (3) or diphenylamino group (4) exhibit high thermal stability and good oxidation-reduction reversibility, which together with their excellent solid-state fluorescence efficiency make them promising bipolar transporting blue emitters. The preliminary results will provide a firm direction for rational design of highly fluorescent solid-state blue emitters with bipolar transporting property.