Strategies for Photochemical and Thermal Modification of Materials

The modification of materials/surfaces is central to numerous applications ranging from opto-electronic devices to biomedical implants and drug delivery. Thus, there exists a high motivation for improving the methodologies which can be employed in order to modify surfaces in a selective and efficient fashion. One of the major goals of surface engineering is to control the chemical composition at the material interface. The fine control of the surface properties is a field of intense research as the performance of functional materials is strongly related to the processes and interactions that are occurring at the materials’ interface. In general, the modification or transformation of surfaces can be achieved via various chemical and physical methods. Although there is a general need for simple and convenient methods to covalently conjugate a molecule of interest to a surface, no single coupling strategy has been broadly adopted. Instead, numerous strategies have been reported in the literature. In an attempt to develop novel strategies to prepare functional materials via surface modifications we examined the potential of a series of photochemical and thermal reactions for such purposes. Methods described in this thesis are divided into two categories: Photochemical and Thermal. In the first chapter, these strategies are introduced. Since many of the modification methods deal with gold nanoparticles (AuNPs), a review of their properties and synthesis methods are also included. Two chapters (chapter 2 and 3) are devoted to the potential of diazirine for photochemical modification of materials and nanomaterials. In chapter 2, diazirine is employed to prepare robust hydrophobic cotton and paper surfaces by coating them with a highly fluorinated phosphonium salt using diazirine as the tether. In chapter 3, the same photochemical modification strategy is extended to nanomaterials by incorporating diazirine onto the surface of water soluble AuNPs. The synthesis and characterization of diazirine-AuNPs is described and it is demonstrated that upon irradiation, the photo generated carbene can be used for the insertion reaction which leads to interfacially modified AuNPs. Starting with chapter 4, we focus on “click-type” and more biologically friendly reactions for surface modification of water soluble AuNPs. Chapter 4 reports our efforts towards modification of small water soluble AuNPs using maleimide interfacial functionality. Both 1,3-dipolar cycloaddition and Diels Alder reactions are studied. In chapter 5, a novel strategy for modification of AuNPs via strain-promoted alkyne-nitrone cycloaddition (SPANC) is introduced. Nitrone functionalized AuNPs are synthesized and characterized. It is demonstrated in this chapter that one can take advantage of the nitrone moiety for interfacial SPANC (i-SPANC) reaction to prepare 18F-radiolabeled AuNPs with potential applications in positron emission tomography (PET). In the second part of chapter 5, the i-SPANC method is further extended to material chemistry by preparing AuNP-carbon nanotube (AuNP-CNT) hybrid nanomaterials