Reversible Dimerization of [5,6]-C₆₀O

Abstract

The recently discovered [5,6]-open isomer of C(60)O has been found to undergo facile dimerization to form a new C(2) symmetry isomer of C(120)O(2), which can be photodissociated with relatively high efficiency to regenerate monomeric [5,6]-C(60)O. High yield dimerization of [5,6]-C(60)O proceeds spontaneously in toluene solution near room temperature. On the basis of (13)C NMR spectroscopy, ab initio quantum computations, and HPLC retention patterns, the resulting C(120)O(2) product has been deduced to be a nonpolar dimer of C(2) symmetry in which the C(60)O moieties are linked by two single bonds between sp(3)-hybridized carbon atoms adjacent to oxygen atoms. Photophysical properties of this dimer have also been measured and compared to those of C(120), the [2 + 2]-dimer of C(60). The ground-state absorption spectrum of C(120)O(2) in toluene is slightly red-shifted relative to that of C(120), with a distinctive peak at 329 nm and an S(1)-S(0) origin band at 704 nm. Its fluorescence spectrum shows two major peaks at 718 and 793 nm. In room-temperature toluene, the measured triplet state intrinsic lifetime of this C(120)O(2) isomer is 34 +/- 2 micros, a value somewhat shorter than that of C(120) (44 micros). C(120)O(2) undergoes photodissociation from its triplet state to regenerate monomeric [5,6]-C(60)O with quantum yields of 2.5% at 24 degrees C and 43% at 70 degrees C. It can therefore serve as a stable reactant for photolytic production of [5,6]-C(60)O. As a simple fullerene adduct that reacts under mild conditions, [5,6]-C(60)O may prove useful in special synthetic applications. Solutions of [5,6]-C(60)O are also unique because they can provide mixtures of a fullerene monomer and its dimer in a dynamic balance controllable by adjustment of concentration, temperature, and optical irradiation.

The influence of oxygen adsorption on the NEXAFS and core-level XPS spectra of the C60 derivative PCBM

“…This appears to be in contrast to studies of C 60 O showing that the formation of the epoxide is more probable. [41][42][43] In our calculations, in fact, if the additional atom is not specifically placed across a 5-6 bond, the PCBM with oxygen relaxes to the epoxide, suggesting a larger energy barrier between the pristine molecule and the [5,6]-PCBM-O even if the overall binding energy is higher in the latter.…”

Peroxide intermediates of oxidation processes: Organic trioxides

“…It results in C 120 O 2 , which is a nonpolar compound with C 2 symmetry. The C 120 O 2 dimer can generate the original oxidoannulene upon photodissociation 306 . The interest in oxidoannulene structures stems from the fact that, despite the chemical transformation of the frame, all the 6,6 double bonds in 5,6-C 60 O remain intact, that is, the unique π-electron system in C 60 does not undergo considerable changes.…”

Fullerene oxides and ozonides

“…Although fullerene ozonides, the initial reaction products, are not stable, their lifetimes are generally long enough to permit purification by high performance liquid chromatography (HPLC). Fullerene ozonides decompose by losing molecular O 2 to form fullerene oxides that differ in structure depending on whether the ozonide dissociation was thermolytic or photolytic [38][39][40]45,46,49]. Gas phase ozonations have also been carried out in mass spectrometers to produce and study large odd-numbered carbon clusters [56,57].…”

“…For a variety of objectives, oxides or their ions were also produced in gas phase studies [7,10,25,26,29,43,56,57,61,[77][78][79][80][81][82][83]. Syntheses using reactants in the solid state have been mainly performed to prepare fullerene multimer oxides such as C 120 O [35,61,[84][85][86], but these compounds have also been produced in solution [32,45,46,87,88]. A rather unusual synthesis of C 120 O m compounds was carried out by the decomposition of C 60 Br 24 in air [89].…”

“…Although Fusco et al [59] had sufficient masses of C 60 O, C 60 O 2 , and C 60 O 3 to determine their solution phase absorptivities, the values seem not to have been reported. Richter et al [16] used 'approximate' but unspecified absorptivities for C 60 [49,92], the C 60 O annulene (42,000 dm mol -1 cm -1 at 336 nm) [49], and C 120 O 2 (115,000 dm 3 mol -1 cm -1 at 329 nm) [45,46]. Because the yield of C 60 O epoxide from thermolysis of the C 60 O 3 ozonide is nearly 100%, it is possible to deduce the absorptivity of the ozonide as 44,000 dm 3 mol -1 cm -1 at 325.8 nm [38].…”