Dinuclear Transition-Metal Terpyridine Complexes with a Dithienylcyclo- pentene Bridge Directed toward Molecular Electronic Applications Yu-Wu Zhong, Neus Vila, Jay C. Henderson, Samuel Flores-Torres, and He ´ctor D. Abrun ˜ a* Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell UniVersity, Ithaca, New York 14853-1301 Received September 11, 2007 A series of dinuclear metal terpyridine (M-tpy; M ) Ru, Os, Fe, and Co) complexes with a photochromic dithienylethene bridge were designed and synthesized through either a convergent or a divergent approach. The open forms of the complexes containing Ru II and Fe II centers were found to be inert to ultraviolet photoirradiation but could be cyclized electrochemically as revealed by a cyclic voltammetric study. On the contrary, the Co II complex underwent efficient photochemical but not electrochemical cycliza- tion. The corresponding Os II complex was neither photochromic nor electrochromic. Stimulated by their potential application in molecular elec- tronics and information storage, chemists have been devoted to the design and synthesis of smart materials that may perform a molecular switch function. 1 Upon response to ex- ternal stimuli, these materials can exhibit both “on” and “off” states, which modulate both their chemical and physical prop- erties. Among these materials, the photochromic dithienyl- ethene derivatives have received much attention as switch materials mainly because of their good fatigue resistance and thermal irreversibility. 2 Simple irradiation with a specific wavelength of light can “switch” the molecule between a nonconjugated open form and a conjugated closed form. Recently, we 3 have been involved in the development of single molecular electronic devices incorporating transition- metal terpyridine (M-tpy) complexes designed so that electron transport occurs through well-defined charge states of the metal center. The M-tpy complexes were selected because of their appealing photophysical and electrochemical properties. 4 The reliable formation of a linear structure via functionalization at the 4′ position of the tpy ligand helps to form a good connection between two electrodes. We are now interested in introducing the photochromic dithienylethene unit into these structures by aiming to control the conductiv- ity of the molecular wire through both photo- and electro- chemical switching. The photochromic properties and con- ductivity switching of dithienylethene derivatives attached on an electrode surface have been studied recently; 5 however, the incorporation of transition-metal complexes into these devices to enhance electron transport remains unexplored. The prototype molecules for our purposes are the dinuclear M-tpy complexes 1-4 bearing a dithenylcyclopentene bridge (Figure 1). Subsequently, anchoring groups such as pyridine, thiolate, or isocyanide will be attached onto the two distal positions of the complexes, and the whole molecules will be used in single-molecule devices. It should be noted that a number of metal polypyridine complexes with a bridging or pendant dithienylethene unit have been reported in studies of the luminescence switch, controlled electron transfer, or metal-metal communication. 6 However, the M-tpy com- plexes containing the dithienylethene unit have not been well investigated partially because of the synthetic difficulties and * To whom correspondence should be addressed. E-mail: hda1@ cornell.edu. (1) (a) Nishihara, H. Bull. Chem. Soc. Jpn. 2005, 77, 407. (b) Habuchi, S.; Ando, R.; Dedecker, P.; Verheijen, W.; Mizuno, H.; Miyawaki, A.; Hofkens, J. Proc. Natl. Acad. Sci. 2005, 102, 9511. (c) Saha, S.; Stoddart, J. F. Chem. Soc. ReV. 2007, 36, 77. (d) Kay, E. R.; Leigh, D. A.; Zerbetto, F. Angew. Chem., Int. Ed. 2007, 46, 72. 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A.; Andre ´asson, J.; Straight, S. D.; Gust, D.; Moore, T. A.; Moore, A. L.; Li, J.; Sankey, O. F.; Lindsay, S. M. Nanotechnology 2005, 16, 695. (d) Duliæ, D.; van der Molen, S. J.; Kudernac, T.; Jonkman, H. T.; de Jong, J. J. D.; Bowden, T. N.; van Esch, J.; Feringa, B. L.; van Wess, B. J. Phys. ReV. Lett. 2003, 91, 207402. Figure 1. Dinuclear complexes studied. Inorg. Chem. 2007, 46, 10470-10472 10470 Inorganic Chemistry, Vol. 46, No. 25, 2007 10.1021/ic701784b CCC: $37.00 © 2007 American Chemical Society Published on Web 11/14/2007