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Pure Appl. Chem., 2011, Vol. 83, No. 4, pp. 779-799

Published online 2011-03-18

Luminescent acetylthiol derivative tripodal osmium(II) and iridium(III) complexes: Spectroscopy in solution and on surfaces

Srinidhi Ramachandra1, Federico Polo2, Fabio Edafe3, Klaus C. Schuermann2, Christian A. Nijhuis4, Peter Belser3*, William F. Reus4, George M. Whitesides4 and Luisa De Cola1,2*

1 Laboratory of Supramolecular Chemistry and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
2 Westfälische Wilhelms-Universität Münster, Physikalisches Institut, Mendelstraße 7, 48149 Münster, Germany
3 Department of Chemistry, University of Fribourg, Chemin du Musée 9, 1700 Fribourg, Switzerland
4 Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA

Abstract: Luminescent Os(II) and Ir(III) complexes containing a tripodal-type structure terminalized with three thiol derivatives are described. The tripod is introduced through derivatization, with a rigid spacer, of a phenanthroline ligand coordinated to the metal ion, and the entire structure possesses axial geometry. The geometry of the complexes combined with the three anchoring sites, the thiol groups, allows the complexes to adopt an almost perpendicular arrangement to the surfaces and the formation of a well-packed monolayer on Au substrates. The photophysical and electrochemical behavior of the complexes is studied in solution and on surfaces. Furthermore, a self-assembled monolayer (SAM) of Os(II) complexes on an ultraflat Au surface is used to fabricate a metal–molecule–metal junction with Au and In Ga eutectic as electrodes. The Os(II) SAM in the tunneling junction exhibits rectification behavior which is opposite in direction to that which we have previously shown for Ru(II) SAMs.