Optically active helical structure and magnetic interaction of poly(phenylacetylene)-based polyradicals Takashi Kaneko a, * , Hiroo Katagiri b , Yasuhiro Umeda b , Takeshi Namikoshi a,c , Edy Marwanta a,c , Masahiro Teraguchi a,d , Toshiki Aoki a,b,c,d a Center for Transdisciplinary Research, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan b Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan c Venture Business Laboratory, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan d Institute of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan article info Article history: Available online 12 January 2009 Keywords: Conjugated polymer Polyradical Phenoxyl Polyacetylene Circular dichroism Helical polymer abstract We synthesized optically active polyradicals possessing an excess of one-handed helical backbone by helix-sense-selective polymerization (HSSP) of achiral monomers which was promoted by rhodium com- plex catalyst in the presence of (R)- or (S)-1-phenylethylamine. The monomer, which had two hydroxy groups and a hydrogalvinoxyl unit, gave the corresponding polymer with an optically active helical con- formation stabilized by intramolecular hydrogen bonding. The chemical oxidation of the polymer yielded the corresponding optically active helical polyradical with high spin concentration. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer. We have found that the stronger antiferromagnetic interaction was observed for the polyradical synthesized by HSSP in com- parison with the polyradical via polymerization in the presence of racemic phenylethylamine. Ó 2008 Elsevier Ltd. All rights reserved. Optically active helical polymers promise interesting technolog- ical applications in optical resolution, chiral sensors, chiroptics, microelectronics and chiral magnets due to the disymmetric nat- ure of one-handed helical sense [1]. In particular, the optical activ- ity of helical p-conjugated polymers will be possible candidates in combination with optic, electronic and magnetic properties. We have already succeeded in synthesizing a p-conjugated polyradical which has high durability to spin defects and a large average S va- lue (S = 5/2) corresponding to the ferromagnetic spin coupling net- work spreading throughout the p-conjugated chain [2]. Our goal is the development of new polyradicals with electronic, magnetic and chiroptical properties through the fusion with optically active helical polymers and the control of hierarchical structures. We have synthesized various optically active helical polyacetylenes, which are typical p-conjugated polymers, by polymerization of the corresponding monomers with chiral side groups [3–11], and by helix-sense-selective polymerization (HSSP) of achiral mono- mers using a chiral catalyst system, i.e. polymerization using rhodium complex catalysts in the presence of (R)-1- or (S)-1-phen- ylethylamine (PEA) [12–17]. The HSSP is a possible method of obtaining various enantiomeric helical polymers since the process demands no chiral moiety in the monomer. This fact will give increased flexibility to monomer design, besides obvious economic implications due to using only a catalytic amount of chiral com- pounds that are often expensive. Actually, we have succeeded in synthesizing optically active helical poly(phenylacetylene)s, poly(1a) [14–16] and poly(2) [17], bearing hydrogalvinoxyl moie- ties for investigation of their magnetic and chiroptical properties by the HSSP of the corresponding achiral monomers (Scheme 1). The helical chirality of the polymers was kinetically stabilized by the achiral side group’s own bulkiness for poly(1a), and by intra- molecular hydrogen bonds among hydroxyl groups in the polymer for poly(2a) although the obtained polymers possess no chiral moi- eties except for helicity. In this study, we synthesized optically ac- tive helical poly(phenylacetylene)-based polyradicals poly(1b) and poly(2b) via HSSP of the corresponding achiral monomers. The nat- ural optical activity, magnetic optical activity and magnetic inter- action of the polymers were discussed in terms of the circular dichroism (CD) spectra, the magneto-circular dichroism (MCD) spectra and SQUID measurements, respectively. The polymerization of 1a was carried out in ethanol/(R)-PEA (9/ 1 v/v) in the presence of [Rh(cod)Cl] 2 (cod = 1,5-cyclooctadiene) catalyst. A red solid polymer poly(1a)(M w = 2.2 Â 10 4 , M w /M n = 1.7) was obtained by precipitation from the polymerization mix- tures into hexane. The monomer 2a was polymerized using Rh + (nbd)[(g 6 -C 6 H 5 )B À (C 6 H 5 ) 3 ] (nbd = 2,5-norbornadiene) catalysts, chiral PEA cocatalyst, and CuI cocatalyst in toluene at 0 °C. The red solid polymers of poly(2a)(M w = 2–8 Â 10 5 , M w /M n = 2–15) 0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.10.067 * Corresponding author. Tel./fax: +81 25 262 6909. E-mail address: kanetaka@gs.niigata-u.ac.jp (T. Kaneko). Polyhedron 28 (2009) 1927–1929 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly