Ali Ahmadpour Fullerenes Ali Ahmadpour Department of Chemical Engineering Faculty of Engineering Ferdowsi University of Mashhad 2014
World of Carbon Materials 2
Fullerenes 1985 Robert F. Curl Jr. Richard E. Smalley Sir Harold W. Kroto 3
Ali Ahmadpour Fullerenes C 60 has been the most thoroughly studied member of fullerenes because it: (1) is produced abundantly in the carbon soot by the arc discharge of graphite electrodes, (2) has high symmetry (with all 60 carbons chemically equivalent), (3) is less expensive, (4) is relatively inert under mild conditions, and (5) shows negligible toxicity. 4
Cont. Ali Ahmadpour Electronically, C60 is described as having a closed-shell configuration, consisting of 30 bonding molecular orbitals with 60 π electrons, which makes C60 a fairly good electron acceptor with the ability of reversibly gaining up to six electrons upon reduction. This high degree of symmetry of C60 provides the foundation for physicochemical, electronic, and magnetic properties. Semiconducting, magnetic, and superconducting properties of unmodified C60 have been intensively investigated. 5
Cont. Ali Ahmadpour The skeleton of C60 consists of 20 hexagonal and 12 pentagonal rings fused all together. Cycloaddition reactions have been widely applied for the functionalization of fullerenes. The special characteristics of the added groups, coupled with the unique structural, physicochemical, and electronic properties of fullerenes, have aided the development of new materials with tremendous potential in widespread technological applications such as electronic and optoelectronic devices, light-emitting diodes photovoltaics, and thermotropic liquid crystals. 6
Functionalization of Ali Ahmadpour Fullerenes Fullerenes behave as 2π electron-deficient and therefore undergo cycloaddition reactions. These have been carried out either thermally or photochemically, and they typically take place on the 6,6-ring junctions of the fullerene skeleton. 7
Cycloaddition C60 dimer 8
Cycloaddition using azomethine ylides Cycloaddition by thermal opening of azyridines 9
Fullerenes functionalized with hydrophilic addends 10
Cycloaddition to C60 11
Generation and reactivity of fullerenecarbenes 12
Self-assembled fullerene architectures Supramolecular architectures containing fullerenes have attracted a lot of attention. Fullerenes can be incorporated into well-ordered arrays by means of different intermolecular interactions, including hydrogen bonding, π-stack interactions, and metal templates. In recent years, novel supramolecular systems have been developed with a wide variety of architectures with very interesting properties. 13
Different interlocked architectures 14
Strategies for the preparation of rotaxanes 15
Hydrogen bond assembled rotaxane 16
Nanorings, Peapods New supramolecular types of fullerenes with concave convex structures have been developed very recently by π-stack interactions. It comprises interactions between fullerenes and different curved carbon structures, such as nanorings or nanotubes. Both structures have π-orbitals oriented radially, as well as the fullerenes. 17
C60-nanoring complex C60 Onion type complex 18
Carbon peapods 19
Yudasaka and coworkers introduced two very interesting and simple methods for the preparation of carbon peapods. These processes are known as nano-extraction and nanocondensation and are easy to apply. First, commercial SWCNTs were treated under extreme conditions to open holes in sidewalls and ends. In nano-extraction, C60 crystallites were sonicated in ethanol, then the nanotubes were added to the solution and left at room temperature for 1 day. TEM images showed (C60)n@SWCNTs in a 50 to 70% filling. In nano-condensation, SWCNTs were deposited on a grid surrounded by filter paper. After the addition of a saturated solution of C60 in toluene, the SWCNTs were filled in at 50 to 70%, in only a few seconds. 20
Applications of Fullerenes In the last few years, scientists have employed different methodologies for the functionalization of fullerenes, as well as different types of supramolecular interactions to build a variety of very interesting molecular architectures with efficient applications. The inherent photo- and electrochemical properties of fullerenes have played an active role in the performance of the system. 21
Applications Ali Ahmadpour Some present and envisioned future applications of fullerene Astrochemistry Batteries Drug delivery Geochemistry Hydrogen storage Lubricant Magnetic resonance imaging contrast agents Medicine Nano ball bearings Solar cells Superconductors Tough protective coatings Trapping reactive species Variety of biological applications DNA photocleavage Neuroprotection Anti-bacterial and anti-virus activity 22
Donor Acceptor systems The research on donor acceptor systems involving fullerenes has attracted a lot of attention, as they can be used as artificial photosynthetic systems to transform light into chemical energy. The simplest systems, known as dyads, can be described as the result of two units, an electron donor (D) and an electron acceptor (A), linked together through covalent or noncovalent interactions. After photostimulation, the charge transfer is induced between the two units leading to a charge-separated state where the energy is stored. 23
(a) Photoinduced electron transfer; (b) radical pair formed 24
Simple fullerene porphyrin dyad 25
Plastic solar cells Fullerenes participate in the formation of chargetransfer complexes with weak electron donors, such as conjugated polymers. Upon photoexcitation, electron transfer takes place between the S 1 excited state of the polymer and the more electronegative C60. The addition of C60 to conjugated polymers increased the photoconductivities to a large extent, as a result of the photoinduced electron transfer. Due to these properties, fullerene-based plastic solar cells (fullerene-based photodiode) are shown as one of the most promising applications of these composite materials. 26
Conclusions The organic functionalization of C60 has produced a wide range of derivatives, which retain the basic properties of fullerene. Among the many possible reactions available, cycloadditions have been most widely used, along with nucleophilic reactions. The products have improved the solubility and processibility and can be used in several applications including electron-transfer reactions, liquid crystals, polymers, dendrimers, and solar cells. The continuous evolution of fullerene science and technology, accompanying the progress obtained in the functionalization chemistry, has led to the production of more and more compounds that open new horizons in the potential applications of these fascinating molecules. 27