Small-Gap Fullerenes from Aldrich Materials Science

Aldrich Materials Science, in partnership with TDA Research, is pleased to introduce purified Small-Gap Fullerenes (SGFs, Table 1). The small band gap properties of these fullerenes are excellent for use in photovoltaic decides as novel solution processable semiconducting materials. Previously, all commercially available fullerenes were recovered from the non- fullerenic carbon matrix by solvent extraction. However, the solvent extraction process is relatively inefficient, as many fullerenes can polymerize into an insoluble state. The polymerization can be mediated by oxygen, but can also occur spontaneously.

Small Gap Fullerenes

Fullerenes with small energy differences between filled and unfilled electronic states of the individual fullerene molecules (“small gap fullerenes”) are especially susceptible to such spontaneous polymerization, and are therefore not recovered by solvent extraction. The percentage of isomers of a certain cage size which are “small gap” increase dramatically as the cage size increases; thus, solvent-extracted fullerenes have few giant fullerenes, while small gap fullerenes (SGFs) are rich in giant fullerenes larger than C₈₄. Despite their relative abundance, SGFs are usually therefore discarded along with the non-fullerenic carbon matrix.

Fullerene Distribution

Figure 1 (below) compares the fullerene distribution of the raw combustion soot with that of the SGF fullerenes and that of conventional solvent-extracted fullerenes. The distributions were generated by time-of-flight mass spectrometry (TOF-MS) using a 355 nm laser pulse to desorb the fullerenes and a 118 nm laser pulse to ionize the fullerenes. Since all fullerenes are ionized with a single 118 nm photon, the distribution depicted is accurate for the fullerenes in the gas phase, although not all fullerenes may be desorbed with equal efficiency. Analysis of the peak heights shows that 60% of the fullerenes present are larger than C₇₀, and 50% of the fullerenes present are larger than C₈₄. (The C₆₀ and C₇₀ remaining appear to have been bound up in the polymers and therefore not extracted by solvents.) SGFs are extremely rich in fullerene cage sizes and isomers which are not present in conventional solvent-extracted fullerenes, including, for example, C₇₄.

Figure 1. Top: Distribution of the small gap fullerene product. Bottom: Distribution of fullerenes recovered by conventional solvent-extraction

Applications of SGF Fullerenes

SGFs may find application both as a fullerenic materials and, following covalent chemical modification, as fullerene derivatives. As received, or following thermal treatment to covert residual hydrocarbon impurities to carbon, SGFs form a novel nanostructured carbon material, which may be useful as a sorbent, catalyst support, or additive to polymeric matrices. Following reduction in a suitable solvent, where the fullerene anions are discrete soluble molecules, SGF films can be electroplated onto a number of substrates to give novel carbon coatings shown in Figure 2.

Figure 2. Electroplated SGF film on Ti foil.

While the chemistry of SGFs remains in its infancy, certain reactions known for C₆₀ can also derivatize SGFs, yielding soluble products. For example, water-soluble polyhydroxylated SGFs (Aldrich Prod. No. 707481) can be useful as water-soluble antioxidants/antiproliferatives. Alternately, organic-soluble SGF esters (Aldrich Prod. No. 707473) shown in Figure 3 can find applications in solution-processable organic electronics as n-type semi-conducting materials.

Figure 3. Left: Water-soluble polyhydroxylfullerene example (Aldrich Prod. No. 707481). Middle: Organic Soluble SGF ester (Aldrich Prod. No. 707473).Right: C₇₄, an example of an un-functionalized SGF (Aldrich Prod. No. 707503).

Conclusion

The SGFs offered here represent the third carbon material, after graphite and diamond, and, considering the technological importance of the first two, a very bright future is forecast for the SGFs as well.

This information has been sourced, reviewed and adapted from materials provided by Sigma Aldrich.

For more information on this source, please visit Sigma Aldrich.