Fullerenes are carbon allotropes including manifold structures such as C60, C70, C76, C78, C84, etc. with sizes ranging from 30 to 3000 carbon atoms. C60 (denoted “buckminsterfullerene” after architect R. Buckminster Fuller) was isolated in 1985 as the first member of this molecular family. The buckminsterfullerene exhibits an aromatic, cage-like, spherical structure with 20 hexagons and 12 pentagons consisting of sp2-hybridized carbon atoms and having a diameter of 7.1 Å.
The unique structures of pristine fullerenes impart many interesting physical properties, such as a high n-type mobility (ca. 10-2−10-1 cm2/ (V·s)) and the impressive ability to withstand reversible electron transfer of up to six electrons. In addition, fullerenes have small reorganization energies upon electron transfer, due to their robust spherical geometry which is also extremely valuable for the application in organic photovoltaics (OPV) devices. OPVs are solar cells fabricated at low temperature and in solution-based processes, which makes them promising candidates for large-area and mechanically flexible solar technology. Fullerenes have been widely used as electron acceptors as early as 1992 in OPVs because of their excellent electrochemical and photophysical properties.
A potential disadvantage for the use of pristine fullerenes in OPVs is their easy aggregation and the resulting moderate or total insolubility in many common organic solvents. Due to this poor miscibility and solubility, it is challenging to form the required bulk heterojunctions in OPVs. Consequently chemically modified forms of C60 (e. g. [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)) were developed. The constructive solution processability has turned PCBM into one of the benchmark acceptor materials for OPVs enabling cell efficiencies of up to 6% in combination with conjugated polymers as poly(3-hexylthiophene) (P3HT). That is why functionalized fullerenes generally prevail as electron acceptors in today`s OPVs.
Additional applications for fullerenes are possible in the fields of material and biomedical sciences. Fullerenes are described as “radical sponges”, since they provide an enormous radical scavenging activity caused by a high electron affinity (ca. 2.7−2.8 eV) and a large number of conjugated double bonds. Therefore, they are powerful antioxidants, reacting readily and at a high rate with free radicals, exhibiting stronger antioxidant performance than current leading antioxidants such as vitamin E. Fullerenes hold great promise in health and personal care applications where prevention of oxidative cell damage or death is desirable (nanomedicine). This leads to the exploration through pharmaceutical companies and development of a series of fullerene-based antioxidant drugs for utilization in neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. Other biological applications mentioned in literature are e. g. the inhibition of various enzymes, cytotoxicity against tumor cells, DNA-cleaving activity through photoinduced formation of superoxide radicals or the use of gadolinium containing metallofullerenes as new magnetic resonance imaging (MRI) contrast agents. In materials science fullerenes have been widely exploited regarding the thermal and thermo-oxidative stabilization of polymeric materials against radical-mediated degradative processes and as protection of organic materials from high-energy radiation (X-ray).
IoLiTec offers a wide range of different fullerenes with high purities at reasonable prices. Our extensive selection covers pristine C60 and C70 as well as numerous derivatised fullerenes for special applications. Standard sizes are in stock and can be delivered within very short times. Larger quantities can be ordered on request.
Text: IOLITEC GmbH, 2013.