Synthesis and Properties of Bipolar Ladder-Like Polysiloxane with Carbazole and Triphenylphosphine Oxygen Groups

In this study, a series of ladder-like polysiloxanes are synthesized by introducing double-chain Si-O-Si polymer as the backbone and the carbazole and triphenylphosphine oxide with high triplet energy as side groups. The ladder-like structures of polysiloxanes are achieved through a controlled polymerization method that involves the monomer self-assembly and subsequent surface-restricted solid-phase in situ condensation through freeze-drying. The introduction of siloxane improves thermal stability of the polymers and inhibits the conjugation of the polymers between the side groups, leading to an increase in the triplet energy level. Therefore, all these polymers perform higher triplet energy levels than phosphorescent emitter (FIrpic). The cyclic voltammetry measurements demonstrate that the bipolar polymer exhibits a high highest occupied molecular orbital (HOMO) value of -5.32 eV, which is consistent with the work function of ITO/PEDOT:PSS, consequently facilitating hole injection. Furthermore, the incorporation of triphenylphosphine oxide promotes electron injection. Molecular simulations reveal that the frontier orbital distributions of the bipolar polymer are located on the carbazole and triphenylphosphine groups, respectively, which facilitate the transport of electrons and holes.