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 materialssthe 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 π-π 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 π-π stacking enhanced the film forming ability. 2PPPF is an amorphous blue light emitter, with a T_g over 100 *C and T_d over 430 *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/m².