Assembly of Platinum Diimine Dithiolate Complexes onto Hydrogen- Terminated Silicon Surfaces Gilles Yzambart, † Bruno Fabre,* ,† Thierry Roisnel, † Vincent Dorcet, † Soraya Ababou-Girard, ‡ Cristelle Meriadec, ‡ and Dominique Lorcy* ,† † Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite ́ de Rennes 1, 35042 Rennes Cedex, France ‡ Institut de Physique de Rennes, De ́ partement Mate ́ riaux et Nanosciences, Campus de Beaulieu, UMR 6251 CNRS-Universite ́ de Rennes 1, 35042 Rennes Cedex, France * S Supporting Information ABSTRACT: The synthesis and structural characterization of the platinum diimine dithiolate complexes [Pt(R 2 bipy)(dmipi)] (dmipi = 4,5-dimercapto-l,3-dithiol-2-propargylimino and R = H, tBu) are described together with the X-ray crystal structure of the dithiolate proligand. These heteroleptic Pt complexes have been covalently bound to hydrogen-terminated silicon (100) surfaces using either a one-step or two-step procedure. The redox-active organometallic film modified surfaces were prepared from a hydrosilylation reaction at 90 °C of either the Pt complex bearing an ethyne terminal group or an ethyne-terminated dithiolate precursor followed by the subsequent anchoring of the Pt complex. Cyclic voltammetry measurements showed the presence of a single reversible one-electron- oxidation process corresponding to the oxidation of the complex into its radical cation species at 0.42 and 0.46 V vs SCE for the unsubstituted and tBu-substituted bipyridine dithiolate Pt complex-modified Si(100) surfaces, respectively. Such values compare well with those determined for the electroactive molecules in solution. Moreover, FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements were consistent with the expected structure of grafted molecular chains and revealed a significant oxidation of the underlying silicon surface. Nevertheless, the one-step procedure was found to lead to redox-active films of density higher than those produced from the two-step procedure. From XPS data, the surface coverage was estimated at 0.10 and in the range 0.03-0.06 Pt complex per surface silicon atom for the one-step and two-step procedures, respectively. ■ INTRODUCTION The integration of redox-active molecules into highly densely packed monolayers covalently bound to hydrogen-terminated silicon (Si-H) surfaces has received intense attention due to the large extent of potential applications of controlled and robust organic/Si interfaces. 1-5 Various electrochemically oxidizable electrophores, such as ferrocene, 6-13 metal-com- plexed porphyrins, 14-18 and tetrathiafulvalenes (TTF), 19-21 have been immobilized onto Si-H using different grafting procedures (hydrosilylation, aryldiazonium, “click”, and carbo- diimide chemistry). The two latest electrophores exhibit multiple electron transfer steps at relatively low potentials and chemical stability of the different redox states. Such attractive characteristics are appealing for the fabrication of electrically addressable devices, particularly when the goal is integrated systems devoted to information storage or transfer. In addition to metalloporphyrins, which exhibit a versatility of their redox properties depending on the nature of the complexed metal, heteroleptic metal dithiolate complexes of the type [M(S ∧ S)(L) n ] in this aspect open wide possibilities as multiredox systems. Indeed, their electrochemical properties can be finely tuned depending on both the nature of the complexed metal and the second type of coordinated ligand (L). 22-24 Among the various heteroleptic dithiolate complexes, Pt complexes of the type [Pt(NN)(S ∧ S)] with a diimine ligand (NN) such as bipyridine (bipy) or 4,4′-di-tert-butyl-2,2′- bipyridine (tBu 2 bipy) have received a great deal of attention as solar cell sensitizers 25 and second-order nonlinear optical (SONLO) materials. 26 These Pt complexes exhibit multistage electrochemical processes; for instance, [Pt(tBu 2 bipy)(dmid)] (dmid = 4,5-dimercapto-l,3-dithiol-2-one) 27 (Chart 1) under- goes two sequential reversible monoelectronic oxidation processes and one reversible monoelectronic reduction step Special Issue: Organometallic Electrochemistry Received: January 14, 2014 Chart 1 Article pubs.acs.org/Organometallics © XXXX American Chemical Society A dx.doi.org/10.1021/om5000369 | Organometallics XXXX, XXX, XXX-XXX