Palladium-Catalyzed Direct Synthesis, Photophysical Properties, and Tunable Electroluminescence of Novel Silicon-Based Alternating Copolymers

A new class of silicon-based alternating copolymers with a uniform π-conjugated segment regulated by organosilicon units was synthesized using the Heck reaction between distyrylsilane monomers and appropriate arylene dibromides. The incorporation of organosilicon units with the aromatic or aliphatic groups on the silicon atoms into π-conjugated systems improved their processability and interrupted the π-conjugation length. They could be spin-cast onto various substrates to give highly transparent homogeneous thin films. Their glass transition temperatures were in the range 94−127 °C. They show strong absorption bands around 356−416 nm, which corresponds to the π−π* transition of the conjugated segments. The maximum photoluminescence appeared around 440−526 nm in the blue or green emission region. Their optical properties depend on the arylene dibromides in the Heck reaction. The single-layered light-emitting diode of an Al/SiPhPPV or SiHMPPV/ITO glass exhibits a threshold voltage of 10−12 V from the I−V curve. The electroluminescence (EL) of the SiPhPPV or SiHMPPV gives an emissive peak at 450 nm. Furthermore, the multilayered light-emitting diodes of an Al/LiAl/SiPhPVK/PANI/ITO glass and an Al/LiAl/SiPhFPV or SiHMFPV/ITO glass shows a threshold voltage of 6−12 V. The EL device based on SiPhPVK exhibits the blue emissive color at 467 nm, when an operating voltage of 7 V was applied. When an operating voltage of 11 V was applied, however, the EL device emits a white color. The EL spectra of the SiPhFPV and SiHMFPV polymers, obtained at an applied voltage of 12 V, show two strong peaks in the blue emissive region as well as in the green region.