Surface Chemistry DOI: 10.1002/anie.200603599 Self-Assembled Monolayers of a Multifunctional Organic Radical** Nfflria Crivillers, Marta Mas-Torrent, Sandrine Perruchas, Nans Roques, JosØ Vidal-Gancedo, Jaume Veciana, Concepció Rovira,* Lourdes Basabe-Desmonts, BartJan Ravoo, Mercedes Crego-Calama,* and David N. Reinhoudt The ultimate goal of molecular bottom-up approaches is to employ functional building blocks to construct nanometer- scale devices that address specific applications. [1] Further- more, immobilization of functional molecules on suitable surfaces is also often required for implementation of a practical device. One powerful and versatile strategy for the modification of surfaces at the molecular level is by the preparation of self-assembled monolayers (SAMs). [2] Although most attention has focused on SAMs of thiols on gold, [3] the use of glass, quartz, or silicon (namely, SiO 2 ) substrates offers clear advantages for preparing SAMs since these systems exhibit superior stability, are compatible with established silicon technologies, and allow the use of optical techniques as read-out mechanisms. [4] Molecules with a variety of functionalities have previously been anchored on SiO 2 surfaces for the fabrication of chemical sensors, [5] the immobilization of biomolecules, [6] the coordination of metals, [7] the preparation of surfaces with nonlinear optical properties, [8] andthemanipulationofthesurfacewettability. [9] ThepreparationofSAMsoforganicradicalsisveryappealing since these systems would provide magnetic functionality to the surfaces. However, there appear to be extremely few examples of SAMs based on organic radicals in the liter- ature [10] and,toourknowledge,organicradicalshavenotbeen previouslyanchoredontoSiO 2 substrates. Here, we describe the functionalization of silicon oxide based surfaces with polychorotriphenylmethyl (PTM) radi- cals. [11] These stable radicals are colored and also exhibit fluorescence in the red region of the spectra. More interest- ingly, PTM radicals are electroactive and can be easily and reversiblyreduced(oroxidized)totheiranionic(orcationic) species. [12,13] The oxidized and reduced states show different absorptionspectrathantheradicalandarealsononmagnetic and nonfluorescent. Therefore, the preparation of SAMs functionalized with PTM radicals (PTM SAMs) on solid substrates results in multifunctional surfaces with electro- chemical, optical, and magnetic activities. Here we also demonstrate that these SAMs can be used as chemical redox switches with optical (absorption and fluorescence) andmagneticresponses. ThestrategyemployedtofabricatethePTMSAMsona SiO 2 surface is depicted in Figure1. The substrate was functionalized with a monolayer of silane molecules with a terminal chemical group that acts as a recognition site. Subsequently, two different PTM radical derivatives are immobilized on the substrate either by covalent or non- covalentinteractions. In our first approach, we prepared a SAM of N-[3- (trimethoxysilyl)propyl]etylenediamine(S1)onSiO 2 surfaces following the procedure previously described. [14] The sub- strates functionalized with the amino-terminated monolayer were immersed in a solution of the tetradecachloro-4- (chlorocarbonyl)triphenylmethyl radical (PTM-COCl) [15] (see Experimental Section) to give the PTM radical SAM S2 as a result of the formation of a covalent amide bond (Scheme1a). Water contact angles for S1 are in accordance with the values reported in the literature [16] (advancing contact angle (q adv ) = (52.0 Æ 0.3)8 and receding contact angle (q rec ) = (45.5 Æ 0.2)8). The increase in the contact angle values of S2 (q adv = (88.8 Æ 0.3)8 and q rec = (45 Æ 4)8) Figure 1. Schematic drawing of the strategy employed to prepare PTM SAMs. [*] N. Crivillers, Dr. M. Mas-Torrent, Dr. S. Perruchas, Dr. N. Roques, Dr. J. Vidal-Gancedo, Prof. J. Veciana, Prof. C. Rovira Institut de Cincia de Materials de Barcelona (CSIC) Campus de la UAB 08193 Bellaterra (Spain) Fax: (+ 34) 935-805-729 E-mail: cun@icmab.es Dr. L. Basabe-Desmonts, Dr. B.J. Ravoo, Dr. M. Crego-Calama, Prof. D. N. Reinhoudt Laboratory of Supramolecular Chemistry and Technology MESA + Institute for Nanotechnology University of Twente P.O. Box 217, 7500 AE Enschede (The Netherlands) Fax: (+ 31) 534-894-645 E-mail: smct@tnw.utwente.nl [**] This work is part of the European Science Foundation EUROCORES (Programmes SONS-FUN-SMARTS I and II) and was also sup- ported by funds from the DGI, Spain (project EMOCIONa, CTQ2006-06333/BQU), and the EC Sixth Framework Programme MAGMANet NoE (Contract no. 515767-2). N.C. thanks the Minis- terio de Ciencia y Tecnología for a PhD fellowship. Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Angewandte Chemie 2215 Angew. Chem. Int. Ed. 2007, 46, 2215 –2219 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim