Synthesis of an optically active helical poly(1,3-phenyleneethynylene) bearing stable radicals and its chiroptical and magnetic properties |
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Institution: | 1. Center for Transdisciplinary Research, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan;2. Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan;3. Venture Business Laboratory, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan;4. Institute of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan |
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Abstract: | We synthesized an optically active helical poly(1,3-phenyleneethynylene) with pendant galvinoxyl residues and dimethyl(10-(1S)-pinanyl)silyl groups. The hydrogalvinoxyl precursor polymer was given by polymerization of (1,3-diiodophenyl)hydrogalvinoxyl and 1,3-diethynyl-5-dimethyl(10-(1S)-pinanyl)silyl]benzene using Pd(PPh3)4 catalyst (Mw = 1.7 × 105, Mw/Mn = 3.7). In the CD spectrum taken in ethyl acetate solution, clear Cotton effects were observed in the absorption region of the backbone and hydrogalvinoxyl chromophore, indicating an excess of one-handed helical foldamer conformation. The polymer yielded the corresponding polyradical with high spin concentration by treatment of the polymer solution with PbO2. The Cotton effects appeared in CD spectra of the polymer and polyradical by addition of methanol to the chloroform solution, although the Cotton effects were hardly observed in chloroform. On the other hand, in the MCD spectra of the polymer and polyradical taken in chloroform solution, Faraday effects were observed in the absorption region of the backbone and galvinoxyl chromophore. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer, and showed the antiferromagnetic interaction. |
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