Supramolecular π-π Stacking Pyrene-Functioned Fluorenes: Toward Efficient Solution-Processable Small Molecule Blue and White Organic Light Emitting Diodes

In this paper, we described a new category of solution-processible small molecule organic light emitting materials-the pyrene-functioned diarylfluorenes: 2PPPF and DPPPF. In solution, both of the materials show deep blue emission. In film, their emission largely red-shifted due to strong pi-pi stacking of pyrene groups. 2PPPF, which is quite rigid in molecular structure, bearing only one alkoxyl group, could form smooth film by spin-coating. From the photoluminescence and morphology study, we believe the strong pi-pi stacking enhanced the film forming ability. 2PPPF is an amorphous blue light emitter, with a T-g over 100 degrees C and T-d over 430 degrees C. The good thermal stability is comparable to polymeric light emitting materials. The material shows strong aggregated emission with a broad structureless peak at about 460 nm in film. Electroluminescent devices by spin-coating were successfully fabricated. A single-layered device using 2PPPF as the active material shows a turn on voltage of 4.3 V, brightness over 3600 cd/m(2), and current efficiency up to 1.30 cd/A. When 2PPPF was blended into PVK, the single-layered device takes on deep blue emission with the CIE 1931 coordinates at (0.16, 0.10). Single-layered white organic light emitting diodes using 2PPPF:MEHPPV blend as the bulk emitter had a maximum current efficiency up to 1.84 cd/A and brightness over 5700 cd/m(2).