Synthesis and Characterization of Graphene Oxide-based Ru(II) Hybrids

Abstract

Materials able to manipulate photonic signals at extremely strong excitation fields have enormous importance in optoelectronic and photonics-based fundamental research and technological applications. In recent years, there has been a growing research interest in the rational design and fabrication of nonlinear optical (NLO) media with sufficiently large nonlinear responses so as to be suitable for practical optical limiting (OL) applications. Graphene oxide (GO)-based surfaces are chemically tunable multifunctional carbon platforms which exhibit multiple types of third-order optical nonlinearities and interesting OL responses that can be further tuned by modifying the sp2 and sp3 carbon content. Specifically, they can be integrated with other complementary NLO moieties via covalent or non-covalent surface functionalization strategies to construct multifunctional hybrid architectures with greater NLO and/or OL performance than the sum of that of the individual components or their physical blends. So far, a variety of different transition metal moieties have been successfully anchored onto the GO-based scaffold to enhance their optical nonlinearities, but examples of transition metal alkynyl complexes (particularly Ru(II) phenylalkynyl complexes) in GO based hybrids in which the two functional moieties are connected via a pi-delocalizable phenylalkynyl bridge are non-existent. Therefore, this thesis explores different covalent functionalization strategies that can be used to rationally integrate the Ru(II) alkynyl moieties onto GO-based carbon platforms. Two different diazonium-based covalent synthetic approaches were assessed to introduce Ru(II) moieties onto the RGO (reduced graphene oxide) surface via phenylalkynyl spacer groups. Alkyne-Co2(CO)6 complexation was studied as a convenient and versatile spectroscopic tool with the aid of FT-IR spectroscopy to probe alkyne grafting on sp2-bonded carbon surfaces, which is often difficult to confirm by other methods. In order to introduce the fundamental concepts related to the work presented here, Chapter 1 contains a brief introduction to the fundamentals of NLO and an overview of the third order NLO effects contributing to OL. Following this, some of the interesting third-order NLO studies of Ru(II) phenylalkynyl complexes are summarized, highlighting their potential in OL applications. Synthesis and surface chemistry of GO and RGO and an in depth review of the third-order NLO and OL properties of hybrids consisting of GO/RGO covalently functionalized by coordination complexes are presented in Chapter 2, together with an emphasis on their heterogeneous NLO mechanisms contributing to the OL process. In Chapter 3, the synthesis and characterization of functionalized graphitic platforms, GO and RGO, from precursor multi-layered graphite are discussed following their OL properties. Chapter 4 includes a discussion of the diazonium coupling-based covalent synthetic approaches that apply to introduce Ru(II) moieties onto the RGO surface via phenylalkynyl spacer groups. Show more