Studies of the stability and potential applications of pyrrolidinofullerenes and other fullerene derivatives

Over the last decade, the variety of chemically modified fullerenes and their potential applications has increased significantly. Among fullerene derivatives, pyrrolidinofullerenes are one of the most widely synthesized types since they can be easily and efficiently obtained via simple reactions from both empty and endohedral fullerenes. Although fullerenes in general and pyrrolidinofullerenes in particular have been considered for numerous applications in electronic and optoelectronic devices, photovoltaics, medicinal chemistry, etc., their potential application in the evolving field of molecular electronics has not been extensively explored. The envisioned role of the fullerenes usually involves storage or transport of electrons. Therefore, studies of the stability of fullerene derivatives under electron-oxidizing and electron-reducing conditions are extremely important. In this dissertation, the potential application of pyrrolidinofullerenes in molecular electronics is addressed. Also, an extensive proton nuclear magnetic resonance ( 1H NMR) characterization of pyrrolidinofullerenes and the stability of different functionalized fullerenes under electrochemical reducing and oxidizing conditions are investigated.;In Chapter 1, the potential use of fullerenes in single-molecular electronic devices is discussed. After a brief discussion of the measurement techniques involved in molecular electronics, the design of a pyrrolidinofullerene-based molecular junction suitable for single-molecule transistor applications is described. This molecular junction employs a pyrrolidinofullerene molecule, in particular trans-1 pyridylpyrrolidino[60]fullerene, which possesses a number of unique properties such as the ability to chemically connect to two electrodes at the same time with a nearly linear geometry. A comprehensive synthetic approach toward trans-1 pyridylpyrrolidino[60]fullerene is given. This approach can also be used for the regioselective synthesis of other pyrrolidinofullerenes. Finally, preliminary conductivity measurements of a fullerene-based molecular junction are discussed.;Chapter 2 describes the thorough 1H NMR characterization of simple pyrrolidinofullerenes. These NMR studies were motivated by the experimental observation that the resonances of the pyrrolidine protons were broadened significantly. The effect of the environment on the appearance of the pyrrolidine proton resonances is investigated in detail. This chapter also includes NMR studies of mixed fullerene bisadducts where one addend is a pyrrolidine-type and the other addend a methano-type.;The ability of pyrrolidinofullerenes, as well as some other functionalized fullerenes, to undergo electrochemical transformations under electron-reducing or electron-oxidizing conditions is investigated in Chapters 3 and 4. Chapter 3 addresses the electrochemical stability of C60 derivatives. First, electrochemical studies of some bismethanofullerenes were conducted and showed, not surprisingly, that these functionalized fullerenes are unstable under reducing conditions. Subsequent studies found that another fullerene species, C60Cl30, was also extremely unstable under electrochemically reducing conditions despite its remarkable thermal stability. Finally, pyrrolidinofullerenes were studied and were found to be unstable under electrochemically oxidizing conditions, leading to the discovery of the electrochemical retro-1,3-dipolar cycloaddition reaction.;Endohedral fullerenes M3N C80 (M= Sc, Y) are discussed in Chapter 4. Similar to empty fullerenes, pyrrolidino derivatives of Sc3N C 80 were found to be unstable under electron-oxidizing conditions and underwent very efficient retro-cycloaddition reactions. The other derivative discussed in this chapter is the product obtained as a result of a cyclopropanation (Bingel-Hirsch) reaction conducted on Y3N C80. This conventional reaction, which normally leads to methano-derivatives on empty fullerenes, gave the first trimetallic nitride endohedral metallofulleroid. The electrochemical, NMR, and X-ray characterizations of this product are discussed in detail.