Azobenzene Derivatives Carrying a Nitroxide Radical Shin’ichi Nakatsuji,* ,² Masahiro Fujino, ² Satoko Hasegawa, ² Hiroki Akutsu, ² Jun-ichi Yamada, ² Vladimir S. Gurman, ‡ and Andrey Kh.Vorobiev* ,‡ Department of Material Science, Graduate School of Material Science, UniVersity of Hyogo, 3-2-1 Kouto, Kamigori, Hyogo 678-1297, Japan, and Department of Chemistry, Moscow State UniVersity, Leninskie Gory, Moscow 119992, Russia nakatuji@sci.u-hyogo.ac.jp; VorobieV@excite.chem.msu.ru ReceiVed NoVember 2, 2006 Several trans-azobenzene derivatives carrying a nitroxide (aminoxyl) radical (2a, 6a-12a) were prepared, and their photoisomerization reactions to the corresponding cis-isomers were investigated. Although no fruitful results could be obtained for the photoisomerizations of the derivatives with para-subsituents (9a-12a), the unsubstututed derivatives at the para-position (2a, 6a, 7a, 8a) were found to show photoisomerizations by irradiation to give the corresponding cis-isomers (2b, 6b, 7b, 8b), being isolated as relatively stable solid materials, and the change of the intermolecular magnetic interactions was apparently observed by the structural change for each photochromic couple. Introduction There is a continuing trend in the field of molecular-based magnetic materials to develop multifunctional spin systems, 1 and the exploitation of organic photofunctional materials has attracted in this context much attention in recent years. 2 As a precedent example, Iwamura and his collaborators prepared a trans-azobenzene derivative carrying two nitronyl nitroxide groups and reported it to show UV as well as EPR spectral change upon irradiation in solution. 3 Since then, a variety of organic and organometallic photofunctional spin systems have been reported until now, and they include several impressive examples of diarylethene derivatives, 4 spin systems with a ferrocene moiety, 5 or metal complexes with a spiropyran photochromic unit. 6 In the course of our studies to develop novel organomagnetic materials, we have been interested in preparing multifunctional spin systems with conductivity, photofunction- ality, or a liquid crystalline property by using stable radicals, especially nitroxide radicals, as spin sources. As for the spin systems with photofunctionality, we have so far proposed several photoresponsive spin systems by using such photochromic systems as norbornadiene/quadricyclane, spiropyran/merocya- nine, anthracene/dimer, or naphthopyran/merocyanine. Azoben- ² University of Hyogo. ‡ Moscow State University. (1) For recent reviews on molecular-based magnetic materials, see: (a) Magnetic Properties of Organic Materials; Lahti, P. M., Ed.; Marcel Dekker, Inc.: New York, Basel, 1999. (b) Molecular Magnetism; Itoh, K., Kinoshita, M., Eds.; Kodansha/Gordon and Breach Science Publishers: Tokyo, 2000. (c) Structure and Bonding, Vol. 100, π-Electron Magnetism: From Molecule to Magnetic Materials; Veciana, J., Ed.; Springer-Verlag: Berlin, 2001. (d) Magnetism: Molecules to Materials; Miller, J. S., Drillon, M., Eds.; Wiley-VCH: Weinheim, Germany, 2001-2005; Vols. I-V. (2) Cf. Natatsuji, S. Chem. Soc. ReV. 2004, 33, 348. (3) Hamachi, K; Matsuda, K.; Itoh, T.; Iwamura, H. Bull. Chem. Soc. Jpn. 1998, 71, 2937. (4) Cf. Matsuda, K.; Irie, M. J. Photochem. Photobiol., C 2004, 5, 169 and references therein. (5) (a) Ratera, I.; Ruiz-Molina, D.; Vidal-Gancedo, J.; Wurst, K.; Daro, N.; Le ´tard, J.-F.; Rivira, C.; Veciana, J. Angew. Chem., Int. Ed. 2001, 40, 919. (b) Ratera, I.; Ruiz-Molina, D.; Vidal-Gancedo, J.; Novoa, J. J.; Wurst, K.; Le ´tard, J.-F.; Rivira, C.; Veciana, J. Chem.sEur. J. 2004, 10, 603. (6) Be ˆnard, S.; Riviere, E.; Yu, P.; Nakatani, K.; Delouis, J. F. Chem. Mater. 2001, 13, 159. 10.1021/jo062266f CCC: $37.00 © 2007 American Chemical Society J. Org. Chem. 2007, 72, 2021-2029 2021 Published on Web 02/20/2007