Functionalized Fullerenes

Unique chemistry and physics of fullerene (C60) materials continue to stimulate advances in applied and fundamental science. Fullerenes are known as excellent electron acceptors and can be chemically modified to improve solubility in organic solvents. Such soluble fullerene derivatives are known as some of the best n-type organic semiconductors1. Moreover, molecular heterojunctions made by covalently linking fullerenes with electron donating or photoactive macromolecules show promise as intrinsic p/n-type semiconductors and even artificial mimics of biological photosynthesis2. To help our customers achieve their research breakthroughs in organic electronics, Sigma-Aldrich® is pleased to offer a line of high quality functionalized fullerene products.

Methanofullerene PCBM is one of the most useful n-type organic semiconductors. It can be blended with p-type conjugated polymers to make photovoltaic (PV) cells3,4 and thin-film organic field-effect transistors (OFETs)5. PCBM is soluble in the same organic solvents as excellent p-type semiconductors, for example MDMO-PPV, MEH-PPV and P3HT (Table 1). This simplifies preparation of blends and solution processing of heterojunction PV cells and OFETs. High electron affinity of PCBM results in efficient photoinduced electron transfer from p-type polymers as well as from metal electrodes in biased thin-film OFETs6. Power conversion efficiencies up to ~4.4% were reported for bulk heterojunction PV cells made with PCBM7.

Figure 1: 684430 PCBM ([6,6]-Phenyl-C60 butyric acid methyl ester)

Table 1: Conduction (LUMO) and valence (HOMO) band energies of p- and n-type organic semiconductors available from Sigma-Aldrich4,5.

Covalently linked C60-donor heterojunctions can be used to further enhance performance of PV cells by controlling 3-dimensional molecular architecture in organic polymer-C60 blends8. Many promising molecular heterojunctions are based on N-methylfulleropyrrolidine (MP-C60) covalently linked to molecular or polymeric p-conjugated systems9. Sigma-Aldrich is pleased to offer the un-substituted MP-C60 electron acceptor (product number 668184). This compound can be used as spectroscopic and redox reference for studies of C60-donor conjugates10,11. It may be fruitful to explore the incorporation of MP-C₆₀ as an n-type material in organic semiconductor devices12. In addition, we offer a set of C60-caboxylates that can be used as building blocks for the preparation of your own functionalized C60 macromolecules.

References:

1. Newman, C. R.; Frisbie, C. D. et al. Chem. Mater. 2004, 16, 4436.
2. Functionalized Fullerene Materials: Prato, M. and Martin, N. (Eds.) J. Mater. Chem. 2002, 12, 1931.
3. Coakley, K. M.; McGehee, M. D. Chem. Mater. 2004, 16, 4533.
4. Thompson, B. C.; Kim, Y.; Reynolds, J. R. Macomolecules 2005, 38, 5359.
5. Meijer, E. J.; De Leeuw, D. M. et al. Nat. Mater. 2003, 2, 678.
6. Antopoulos, T. D.; Tanase, C. et al. Adv. Mater. 2004, 16, 2174.
7. Li, G.; Shrotriya, V. et al. Nat. Mater. 2005, 4, 864.
8. Cravino, A.; Sariciftci, N. Nat. Mater. 2003, 2, 360.
9. Roncali, J. Chem. Soc. Rev. 2005, 34, 483.
10. Guldi, D.; Luo, C. et al. J. Phys. Chem. A 2004, 108, 455.
11. Giacalone, F.; Segura, J. et al. Chem. Eur. J. 2005, 11, 4819.
12. MFP is an effective electron acceptor soluble in halogenated organic solvents. See comparison of electrochemical reduction potentials of C60 and MP-C60 in ref. 11.