The photophysical properties of dipyrenylbenzenes and their application as exceedingly efficient blue emitters for electroluminescent devices

Three blue-light emitting dipyrenylbenzene derivatives, 1-(4-(1-pyrenyl)phenyl)pyrene (PPP), 1-(2,5-dimethoxy-4-(1-pyrenyl)phenyl)pyrene (DOPPP), and 1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene (DMPPP), have been prepared by the Suzuki coupling reaction of aryl dibromides with pyreneboronic acid in high yields. These compounds exhibit high glass-transition temperatures of 97-137 degrees C and good film-forming ability. As revealed from single-crystal X-ray analysis, these dipyrenylbenzenes adopt a twisted conformation with inter-ring torsion angles of 44.5 degrees-63.2 degrees in the solid state. The twisted structure is responsible for the low degree of aggregation in the thin films that leads to fluorescence emission of the neat films at 446-463 nm, which is shorter than that of the typical pyrene excimer emission. The low degree of aggregation is also conducive for the observed high fluorescence quantum yields of 63-75%. In organic light-emitting diode (OLED) applications, these dipyrenylbenzenes can be used as either the charge transporter or host emitter. The non-doped blue OLEDs that employ these compounds as the emissive layer can achieve a very high external quantum efficiency (eta(ext)) of 4.3-5.2%. In particular, the most efficient DMPPP-based device can reach a maximum eta(ext) of 5.2% and a very high luminescence of 40400 cd m(-2) in the deep-blue region with Commission Internationale Enclairage (CIE) coordinates of (0.15, 0.11).