Design, Synthesis And Properties Of Functional Conjugated Polymer Materials

Six series of new functional conjugated polymeric materials were designed and synthesized,which named as alternating(phenylene vinylene)-(1,4-diketo-3,6-diphenyl pyrrolo[3,4-c]pyrrole)(DPP) copolymers(PDPPPV),alternating (dioctyloxyphenylene ethynylene)-DPP copolymer(PDPPDOPE),alternating (didecyloxyphenylene ethynylene)-triphenylpyrazoline(TPP) copolymer (PTPPDDPE),cationic poly(p-phenylene vinylene) conjugated polyelectrolyte (PPV-N(Et)₃⁺),anionic poly(p-phenylene vinylene) conjugated polyelectrolyte (MPS-PPV),meta-linked anionic poly(p-phenylene ethynylene) conjugated polyelectrolyte(m-PPYPE-SO₃Na) and hyperbranched anionic poly(p-phenylene ethynylene) conjugated polyelectrolyte(HPPE-SO₃Na),respectively.Alternating(phenylene vinylene)-DPP copolymers,were synthesized via Pd-catalyzed Heck cross-coupling polycondensation,and an alternating (dioctyloxyphenylene ethynylene)-DPP copolymer was prepared via cross-coupling polycondensation in the presence of Pd(PPh₃)₂Cl₂ and phase transfer catalysts.All these polymers were characterized by ¹H NMR,IR spectroscopy and elemental analysis.In addition,their UV-Vis and photoluminescence spectra,thermal and electrochemical properties were investigated.It was found that the copolymers exhibited much wider adsorptions in the range of visible light compared with corresponding homopolymers,which may result from the effective charge transfer between the electron donor and electron acceptor segments in the main chain of the copolymers and beneficial for the improvement in optical harvesting efficiency when applied in photovoltaic device.Electrochemical analysis revealed that the two kinds of DPP-containing polymers exhibited a low bandgap(E_g^EC＜1.8eV),and thus they could act as electron acceptor when blended with MEH-PPV and show potential applications as active layer materials in a polymer photovoltaic cell.The PL emission intensity of MEH-PPV is almost completely quenched when blended with the copolymers.Furthermore,the two kinds of copolymers exhibited large Stokes shifts both in solution and as a thin film,and could be promising candidates for fluorescence probe.An anionic poly(p-phenylene vinylene) conjugated polyelectrolyte MPS-PPV and a cationic poly(p-phenylene vinylene) conjugated polyelectrolyte PPV-N(Et)₃⁺ were prepared by Glich dehydrohalogenation polymerization and characterized by ¹H NMR, IR spectroscopy,UV-Vis spectroscopy,photoluminescence spectroscopy and thermogravimetric analysis.The two water-soluble conjugated polyelectrolytes were deposited on interdigitated gold electrodes by dip coating to construct resistive-type humidity sensors,and their humidity sensitive properties at room temperature were investigated over the range of 25-98%RH.It was found that the humidity sensitive properties of undoped anionic polymer MPS-PPV was similar to that of typical saturated polyelectrolytes such as sodium polystyrenesulfonate.In contrast,the LiClO₄-doped MPS-PPV showed different humidity sensing behavior compared with LiClO₄-doped NaPSS.The unusual humidity sensing behavior could be attributed to the influence of oxidative doping agent LiClO₄ on the conjugation structure and conductivity of the polymer MPS-PPV.The cationic polymer PPV-N(Et)₃⁺ exhibited high sensitivity,as characterized by impedance changing almost linearly on a semi-logarithmic scale from 10⁷ to 10⁴Ωwhen humidity decreased from 22 to 97%RH.In addition,moderate hysteresis(～6%RH) was observed.A meta-linked anionic poly(phenylene ethynylene) conjugated polyelectrolyte m-PPYPE-SO₃Na was synthesized via Pd-catalyzed Heck-Sonogashira coupling reaction.Its fluorescence spectra showed concentration- and solvent-dependency due to the aggregation of the conjugated polyelectrolyte in water solution.It was found that surfactants affected the aggregation of the polyelectrolyte.The interactions of cetyltrimethylammonium bromide(CTAB) and poly(vinyl pyrrolidone)(PVP) with m-PPYPE-SO₃Na in aqueous solution promoted the aggregation and broke the aggregation of the conjugated polyelectrolyte,respectively.The PH value of the solution had great influence on the photophysical properties of m-PPYPE-SO₃Na, especially the fluorescence properties.The fluorescence of the polymer in water solution could be effectively quenched by N,N'-dimethyl-4,4'-bipyridinium(Methyl viologen,MV²⁺).Linear fit of the quenching plots afford Stern-Volmer constants(K_sv) of 5.65×10⁵M^-1for intrinsic fluorescence emission of the polymer m-PPYPE-SO₃Na, which is of the same order of magnitude as the meta-linked anionic poly(p-phenylene ethynylene) conjugated polyelectrolyte m-PPE-SO₃Na and suggested its good fluorescence sensitivity.A hyperbranched anionic poly(phenylene ethynylene) conjugated polyelectrolyte HPPE-SO₃Na was synthesized via Pd-catalyzed Heck-Sonogashira coupling reaction. Its fluorescence spectra also showed concentration- and solvent-dependency due to the aggregation of the conjugated polyelectrolyte in water solution.The surfactants interacted with HPPE-SO₃Na in solution in different ways.The addition of CTAB and PVP resulted in the promotion and breaking of the aggregation of HPPE-SO₃Na in solution.The fluorescence of the polymer in water solution could be effectively quenched by N,N'-dimethyl-4,4'-bipyridinium(MV²⁺).Linear fits of the quenching plots afford Stern-Volmer constants(K_sv) of 2.03×10⁵M^-1 and 8.46×10⁵M^-1 for intrinsic and aggregated fluorescence emission,respectively.The fluorescence quenching efficiency of the intrinsic fluorescence emission and aggregation fluorescence emission by(MV²⁺) was about 78 and 328 times greater than that of model monomer PE-SO₃Na,respectively.Further more,metal ions commonly found in biology system could not interfere in the detection of MV²⁺ with HPPE-SO₃Na.Alternating(didecyloxyphenylene ethynylene)-TPP copolymer(PTPPDDPE) was synthesized via Pd-catalyzed Heck-Sonogashira coupling reaction.The UV-vis and PL spectra of the polymer exhibited a significant red shift compared with the monomer triphenylpyrazoline.The Electrochemical bandgap(E_g^EC) and optical bandgap(E_g^OPT) was estimated to 2.37eV and 2.45eV,respectively.It was found that the fluorescence of the polymer solution exhibited a larger red shift when the polarity of the solvent increased.This phenomenon could be attributed to the twist intramolecular charge transfer(TICT) in the main chain of polymer,which suggested its potential applications in a fluorescence probe for micro environment detection.