Synthesis And Optoelectronic Properties Of PPV/PPE-Type Conjugated Polymers Having Backbones Incorporated With N-Heterocycles

In this contribution, five novel conjugated polymers with their backbones incorporated with nitrogen-containing heterocycles were designed and synthesized. They were poly(phenylene ethynylene) C10-PPE-TPP with 1,3,5-triphenyl-2-pyrazoline alternating units; poly(phenylene ethynylene) C10-PPE-DPP and poly (phenylene vinylene) C6DPPDHPV with 3,6-diphenyl-pyrrole[3,4-c] pyrrole-1,4-dione alternating units; poly(phenylene vinylene)s C6DTDPPDHPV and C62DTDPP DHPV with 3,6-dithieno-pyrrole[3,4-c]pyrrole-1,4-dione alternating units. Their molecular structures, photophysical properties, thermostability, aggregation states and electrochemical properties were clearly characterized via NMR, FTIR, GPC, element analysis, UV-vis and photoluminescence spectra, TGA, DSC, X-ray diffraction and cyclic voltammetry. Organic solar cell and thin film field-effect transistor employing diketopyrrolopyrrole-containing polymers as active components were also fabricated and examined.It was found that C10-PPE-TPP was imparted with the twist intramolecular charge transfer characteristic after the conjugated backbone was incorporated with pyrazoline units. Its photoluminescence in solutions exhibited strong solvent polarity dependence. Thanks to the introduction of diketopyrrolopyrrole units into the main chain, the electron and hole injection barriers of C10-PPE-DPP were able to be balanced when it is considered as an electroluminescent polymer applied in display device. In addition, C10-PPE-DPP can also be employed as both polymer electron donor and acceptor in organic bulk heterojunction solar cell with promising photovoltaic responses.It was revealed that the N-alkyl and 3,6-aryl substituents in diketopyrrolopyrrole units played key roles in fine tuning photophysical properties, molecular stacking and electronic structures of the poly(phenylene vinylene)s so prepared, which was proved to exert significant impacts on photovoltaic performance and carrier transport. All three poly(phenylene vinylene)s could be classified as low bandgap polymers, exhibiting strong absorptions covering broad UV-vis region. Differences between the HOMO energy levels of the polymers and the LUMO energy levels of PCBM were approximately proportional to the open circuit voltages of the photovoltaic devices. Among the three polymers, C6DPPDHPV, which showed ordered chain packing as revealed in X-ray diffraction, demonstrated the highest device efficiency of 0.72%. Furthermore, its hole mobility was as high as 5.4x10-4 cm2/Vs when applied as a field-effect transistor material.