Abstract
Three blue-light emitting dipyrenylbenzene derivatives, 1-(4-(1-pyrenyl)phenyl)pyrene (PPP), l-(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 °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°-63.2° 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 (η ext ) of 4.3-5.2%. In particular, the most efficient DMPPP-based device can reach a maximum η ext of 5.2% and a very high luminescence of 40 400 cd m -2 in the deep-blue region with Commission Internationale d'Énclairage (CIE) coordinates of (0.15, 0.11).