Attaching Persistent Organic Free Radicals to Surfaces: How and Why

Organic/inorganic hybrid materials based on attaching functional molecules to a surface are attracting great attention due to the wide range of novel properties and applications that these new materials can bring. Additionally, the use of organic molecules for surface functionalization opens the possibility to tune the material properties and molecular assembly through synthetic chemistry. A particularly appealing field is focused on employing as an active molecular unit an organic free radical to anchor on a substrate either chemically or by physisorption. However, and unavoidably, the first question that arises when an organic free radical is deposited/grafted on a surface is what is the implication of their organization and relative arrangement of the neighboring radicals as well as their orientation with respect to the surface on their properties. Thus, a crucial issue is whether in these surface radical organizations, especially when conducting surfaces are employed, the magnetic properties of the molecules are preserved. This has prompted the application to these systems of several magnetic characterization techniques as well as theoretical studies, and in most of the cases, it has been found that the spin of the molecule is maintained after surface grafting. To further progress in this area, it is imperative to not only synthesize promising functionalmolecules able to form stable and robust surface assemblies but also to develop sensitive characterization techniques to read, or even modify (i.e., write), the surface properties. In most of the reported cases in which the radicals were covalently attached to a surface, hybrid materials exhibiting high robustness were achieved, offering wide perspectives for these materials. Hence, some of the traditional applications of organic free radicals have already been transferred to SAMs of these molecules on surfaces, such as spinprobe and spin-label functions, preparation ofmagneticmaterials, and as catalysts in oxidation processes of organicmolecules. In addition, an emerging and potential application that is growing large expectations is their use for the fabrication of spintronic devices, where the unpaired electron of the free radical could favor spin polarization conservation during the electron transport process. Further, the magnetic properties of bistable radicals have also been successfully exploited as an output signal in surface-confined molecular switches that could in the future lead to single molecule switching devices. In all likelihood, these novel hybrid materials based on attaching organic free radicals on surfaces will continue to arouse the interest of materials scientists in the coming years, since a wide range of interdisciplinary applications are foreseen. © 2011 American Chemical Society.