Novel cyclohexylsilyl- or phenylsilyl-substituted poly(p-phenylene vinylene)s via the halogen precursor route and Gilch polymerization

Abstract

Novel cyclohexylsilyl- or phenylsilyl-substituted poly(1,4-phenylene vinylene) (PPV) derivatives, poly [2,5-bis(dimethylcyclohexylsilyl)-1,4-phenylene vinylene] (BDMCyS-PPV), poly [2,5-bis(dimethylphenylsilyl)-1,4-phenylene vinylene] (BDMPS-PPV), poly [2-dimethylcyclohexylsilyl-1,4-phenylene vinylene] (DMCyS-PPV), and poly [2-dimethylphenylsilyl-1,4-phenylene vinylene] (DMPS-PPV), were synthesized via the bromine precursor route (BPR) and Gilch dehydrohalogenation polyaddition. Thin films of the insoluble BDMCyS-PPV and BDMPS-PPV were fabricated from soluble polymer precursor materials by thermal conversion, and the electronic properties of these films were investigated. Monosilyl-substituted DMCyS-PPV and DMPS-PPV exhibited good solubility in the conjugated state, good film-forming properties, and high molecular weights. Moreover, they showed better thermal stability and higher values of T-g (DMCyS-PPV, 125 degreesC; DMPS-PPV, 127 degreesC) than other PPV derivatives including alkylsilyl-substituted PPVs; this improved mechanical stability led to good electroluminescence performance. Monocyclohexylsilyl- or phenylsilyl-substituted DMCyS-PPV and DMPS-PPV exhibited sharp PL emissions at about 511 and 513 nm, respectively, along with extremely high photoluminescence (PL) efficiencies in both solution and film (DMCyS-PPV, Phi(film) = 0.83; DMCPS-PPV, Phi(film) = 0.82). LED devices fabricated from DMCyS-PPV and DMPS-PPV using the configuration ITO/polymer/Al showed electroluminescence (EL) maxima at 510 and 515 nm, respectively, with external EL quantum efficiencies of 0.02% and 0.03%. Incorporation of PVK as a hole-transporting layer between the ITO and polymer with an air-stable aluminum cathode caused a substantial improvement in the EL quantum efficiencies, increasing the values to 0.07% for DMCyS-PPV and 0.08% for DMPS-PPV.