A solution comprising a polar solvent and C.sub.60 in which the solubility of C.sub.60 is at least 2 mg/ml of solvent. The polar solvent has a low toxicity, high boiling point, high thermal and electrochemical stability, low viscosity, low freezing point, a high dielectric constant, and is relatively inexpensive. Preferably the polar solvent is N-ethyl-2-pyrrolidone.

FIELD OF THE INVENTION 
The present invention is directed to solutions of buckminsterfullerene 
(C.sub.60) and the polar solvent N-ethyl-2-pyrrolidone which are useful 
for the deposition of C.sub.60 via evaporation of the solvent, for the 
preparation of electron transfer complexes of C.sub.60, and for the direct 
electrochemical reaction of unsubstituted C.sub.60. 
BACKGROUND OF THE INVENTION 
Since the announcement of the discovery of C.sub.60, buckminsterfullerene, 
in 1985 ("C.sub.60 : Buckminsterfullerene," H. W. Kroto, J. R. Heath. S. 
C. O'Brien, R. F. Curl, and R. E. Smalley, Nature, Vol. 318, 1985, pp 
162-163) and the announcement of the discovery of a method of producing 
macroscopic quantities of C.sub.60 in 1990 ("Solid C.sub.60 : A New Form 
of Carbon," W. Kratschmer, Lowell D. Lamb, K. Fostiropoulos, and Daniel R. 
Huffinan, Nature, Vol. 347, 1990, pp 354-358), a substantial amount of 
research has been conducted on this recently recognized form of carbon, 
specifically to finding a polar solvent that has a high boiling point, low 
toxicity, a high dielectric constant, high thermal and electrochemical 
stability, low viscosity and freezing point, and is relatively inexpensive 
in which C.sub.60 is highly soluble. In the above cited paper, Kratschmer, 
et al., reported that buckminsterfullerene is soluble in benzene, giving a 
"wine red to brown liquid" (pg. 354). The solubility of C.sub.60 in 
benzene was exploited by authors for the extraction of C.sub.60 from 
condensed soot produced in the electric arc between carbon rods and for 
the deposition of the pure material from benzene solutions. However, 
benzene does not meet the profile of a desired solvent due to it being 
non-polar and a suspected carcinogen. 
In 1993, Ruoff, et al., reported on the solubility of C.sub.60 in a wide 
variety of solvents ("Solubility of C.sub.60 in a Variety of Solvents," R. 
S. Ruoff, Doris S. Tac, R. Malhotra, and D. C. Lorents, Journal of the 
American Chemical Society, Vol. 97, No. 13, 1993, 3319-3323). These 
authors report that C.sub.60 is soluble (up to approximately 50 mg/ml) in 
benzene and naphthalene derivatives, sparingly soluble in substituted 
alkanes (up to approximately 1 mg/ml), and insoluble in polar solvents 
(less than 0.003 mg/ml). These authors concluded that, while solubility 
trends are predictable for various classes of solvents, solubility in any 
particular solvent must be individually tested. This conclusion was 
supported by the exceptionally high solubility (0.89 mg/ml) of C.sub.60 in 
N-methyl-2-pyrrolidone (NWP) considering the authors statement regarding 
the insolubility of C.sub.60 in polar solvents and the high polarity of 
NMP (dielectric constant=32.2). The preparation (i.e., solvent extraction 
of C.sub.60 from condensed carbon-arc soot) and use (i.e., electrochemical 
applications) of C.sub.60 are inhibited to some degree by the very low 
solubility of C.sub.60 in low-toxicity solvents. The solvents in which 
C.sub.60 are most soluble, the chlorinated aromatics (benzene, 
naphthalene, etc.) are suspected carcinogens. Although, the 
electrochemistry of C.sub.60 has been determined through the preparation 
of polar solvent-soluble derivatives or through the use of mixed 
solvents/supporting electrolytes such as those described by Muller and 
Heinze ("Direct Electrochemical Detection of C.sub.60 in Solution by 
Steady-State Voltammetry at Microelectrodes," R. Muller and J. Heinze, 
Journal of the Electrochemical Society, Vol. 145, No. 4, 1998, pp 
1227-1232), the potential electrochemical applications broadly expand if a 
single polar solvent is found. None of the preceding documents disclose a 
polar solvent that meets the aforementioned criteria. In fact, one of the 
above documents teaches that a polar solvent generally will not have a 
high solubility for C.sub.60 regardless of the solvent's other properties. 
SUMMARY OF THE INVENTION 
The present invention is directed to a solution comprising: (a) a polar 
solvent and (b) C.sub.60, wherein the solubility of C.sub.60 in the polar 
solvent is at least 2 mg C.sub.60 per ml of solvent. More specifically, 
the present invention is directed to solutions of buckminsterfullerene 
(C.sub.60) dissolved in N-ethyl-2-pyrrolidone (NEP), 
NEP is a polar solvent that meets all of the aforementioned criteria and 
has a surprisingly high solvency for C.sub.60. The use of NEP as a solvent 
increases the amount of C.sub.60 prepared via evaporation of the solvent 
(after extraction of the solvent from soot or from solutions prepared by 
contact between C.sub.60 and NEP). The C.sub.60 /NEP solutions can also be 
used in the preparation of electron transfer complexes of C.sub.60 (e.g., 
C.sub.60 complexes with TCNQ), and for direct electrochemical reactions of 
unsubstituted C.sub.60. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to a polar solvent for C.sub.60 in which 
C.sub.60 has a surprisingly high solubility and to the solutions of 
C.sub.60 in this polar solvent. Particularly, the present invention is 
directed to a solution comprising: (a) a polar solvent and (b) C.sub.60, 
wherein the solubility of C.sub.60 in the polar solvent is at least 2 mg 
C.sub.60 per ml of solvent, preferably at least 3 mg C.sub.60 per ml of 
solvent, and more preferably at least 5 mg C.sub.60 per ml of solvent. 
The polar solvent should have a low toxicity, a high boiling point and 
dielectric constant, high thermal and electrochemical stability, low 
viscosity, a low freezing point, and be relatively inexpensive. A polar 
solvent that meets the aforementioned criteria and in which C.sub.60 has a 
surprisingly high solubility is NEP-N-ethyl-2-pyrrolidone. The solutions 
are formed by dissolving C.sub.60 in NEP. 
NEP is similar to N-methyl-2-pyrrolidone in many properties. The boiling 
point of NEP is in excess of 200.degree. C. NEP has a high dielectric 
constant (28.2), a low viscosity, below 10 c.p.s., e.g. similar to water, 
and is not presently considered by industry or the federal government as a 
hazardous chemical. 
Amnine salt solutions in 75% NEP/25% cosolvent are known as electrolytic 
capacitor electrolytes and are very thermally and electrically stable as 
indicated by the examples in U.S. Pat. No. 4,812,951. The very low 
freezing point of NEP (below -70.degree. C.) suggests that substantially 
less intermolecular hydrogen bonding is present in NEP than NMP (freezing 
point=-26.degree. C.), giving NEP a pseudo aromatic nature. It is believed 
that this "pseudo-aromatic" nature of NEP facilitates dissolution of 
C.sub.60. 
It was discovered that the solubility of C.sub.60 in NEP exceeded the 
solubility of C.sub.60 in NMP (0.89 mg C.sub.60 /ml NMP). Particularly, 
NEP has a solubility of at least 5 mg C.sub.60 /ml NEP. This is a 
surprising increase of over 500% compared to the solubility of C.sub.60 in 
NMP. The solutions of C.sub.60 in NEP are the wine-red to brown color 
associated with C.sub.60 solutions in the toxic aromatic solvents. 
The use of NEP as a solvent for C.sub.60 facilitates the preparation of 
solutions approximately an order of magnitude more concentrated than NMP 
and over 3 orders of magnitude more concentrated than traditional polar 
organic solvents, e.g. water, alcohols, etc. 
By dissolving C.sub.60 in NEP, greater amounts of C.sub.60 may be obtained 
from low toxicity/high flash point extraction separation of C.sub.60 from 
condensed carbon soots. Generally, the soot and NEP are stirred together. 
The soot is allowed lo settle and the red solution of C.sub.60 is 
decanted. 
The solutions may also be used in the preparation of C.sub.60 films via 
solvent evaporation. C.sub.60 is dissolved in NEP to form a solution. The 
solution its applied to a surface and then the NEP is evaporated to leave 
a film. Heat is desirable to advance the evaporation. Additionally, the 
solutions may be used in the preparation of electrically bistable films 
(for switches, etc.) consisting of C.sub.60 complexes, such as the 
C.sub.60 /TCNQ complexes described by Gao, et. al. 
("Fullerene-Tetracyanoquinodimethane Thin Film and Novel Electrical 
Bistablity," H. J. Gao, Z. Q. Xue, Q. D. Wu, and S. J. Pang, Journal of 
Material Research, Vol. 11, No. 16, 1996, 1996, pp 2192-2194), via a 
solution route. The C.sub.60 /TCNQ complex is dissolved in NEP to form a 
solution. The solution is applied to a surface and NEP is allowed to 
evaporate. The solutions may also be used in electrochemical 
reactions/syntheses involving dissolved C.sub.60 without requiring prior 
derivitization and minimizing solvent decomposition. Various polar 
solvents-soluble species, organic or inorganic or both, may be dissolved 
in NEP-C.sub.60 solutions for electrochemical reaction as graphite or 
platinum electrodes.

EXAMPLE 
5 mg/g C.sub.60 in NEP was prepared by allowing the C.sub.60 to stand in 
contact with the NEP for 72 hours without heating or stirring.