Hindrance-functionalized π-stacked polymer based on polystyrene with pendent cardo groups for organic electronics

Abstract

A hindrance-functionalized π-stacked polymer, poly(4-(9-phenyl-fluoren-9-yl)styrene) (PPFS), was designed and synthesized by the introduction of bulky 9-phenylfluorenyl moieties (PFMs) with 3D cardo structure into all the phenyl units of polystyrene (PS) through the sp³ carbon linkage. The PFMs obviously alter π-stacked conformation and interchain interactions with respect to the precursor PS. The suitable HOMO–LUMO energy gap, high triplet energy, and excellent thermal and morphological stabilities enable PPFS to serve as not only electrically bistable materials but also phosphorescent hosts. Memory devices using PPFS as an active layer exhibited nonvolatile flash memory performance with ON/OFF current ratio up to 10⁴, high stability in retention time up to 10⁴ s and a number of read cycles up to 10⁵ under a read voltage of 1.5 V in both ON and OFF states, while PS based devices exhibited no memory performance. Polymer light-emitting devices (PLEDs) using PPFS as the host and FIrpic as the guest exhibited blue emission with CIE chromaticity coordinates (x, y) of (0.146, 0.349). These results indicate that hindrance-functionalization opens a way to transform commercially available general purpose polystyrenes into functional π-stacked macromolecules.