Synthesis and Characterization of Poly(fluorene)-Based Copolymers Containing Various 1,3,4-Oxadiazole Dendritic Pendants

A series of poly(fluorene)s (PFs) containing different generations of poly(benzyl ether) dendritic wedges with oxadiazole (OXD) peripheral functional groups, including copolymers bearing carbazole (CAZ) pendent groups, were synthesized. The dendritic side-chain polymers possessed excellent solubility in common solvents and good thermal stability with decomposition temperatures of 5% weight loss at more than 370 °C. Photophysical studies reveal that the photoluminescent (PL) properties of the dendronized polymers were greatly affected by the size of the dendritic side chains. The G1- and G2-substituted PF derivatives greatly suppress the aggregation PF backbones and thus to induce pure blue PL emission (with shorter wavelengths than PF). Excitation of the peripheral functional groups leads to substantial energy transfer from the dendrons to the poly(fluorene) backbones. In addition, the excitation of PF bearing G2 dendrons (G2-OXD) at 303 nm creates stronger fluorescence than that at 390 nm, indicating that the intensity of the sensitized emission (by OXD absorption at 303 nm) is even stronger than that of a direct poly(fluorene) emission (by PF backbone absorption at 390 nm). Double-layer light-emitting diode (LED) devices with the configuration of ITO/PEDOT/polymer/LiF/Al were fabricated and reported. The device with PF bearing G0 dendrons and CAZ pendants (G0-OXDCAZ) as an emitter shows a turn-on voltage of 4.5 V and a bright luminescence of 2446 cd/m2 at 12 V with a power efficiency of 0.24 cd/A at 100 mA/cm2.