A precise determination of the triplet energy of carbon (C60) by photoacoustic calorimetry

Fullerenes

“…175 The value of the T\ triplet lifetime varies widely from one study to another, presumably because of the great sensitivity of this lifetime to the presence of oxygen, which has been shown for different solutions to reduce the triplet lifetime from <40 /AS to -3 0 0 ps. 174 ' 176 Despite the difference in the values of the reported triplet T\ lifetimes, it is clear that in the absence of oxygen, the triplet T\ lifetime is much longer than the singlet Si lifetime, so that a metastable T\ state can be established. The significant population of a metastable 7\ level that can be achieved in C 6 o by optical pumping leads to interesting nonlinear optical properties as discussed below.…”

“…It is significant that the lowest energy level of the triplet manifold has been found experimentally to lie about 0.4 eV lower in energy than the lowest energy level of the singlet Si manifold. 174 Also of significance is the long life of the lowest triplet state (>2.8 X 10~4 s) relative to the lowest singlet state (1.2 ns) in the room temperature solution absorption spectra. 175 The value of the T\ triplet lifetime varies widely from one study to another, presumably because of the great sensitivity of this lifetime to the presence of oxygen, which has been shown for different solutions to reduce the triplet lifetime from <40 /AS to -3 0 0 ps.…”

“…132 ' 174 ' 176 However, in the organic glass solvent, the effect of oxygen on the triplet state lifetime is less important because of the lower oxygen diffusion and reduced collision rate. Using photoacoustic calorimetry, 174 the triplet energy E T = 36 kcal/mole or 1.56 eV has been obtained in C 60 . The small singlet-triplet splitting (AE S ,T ~ 9 kcal/mole or 0.4 eV) is consistent with the relatively large diameter of a Qo molecule.…”

A Copper( I )‐Complexed Rotaxane with Two Fullerene Stoppers: Synthesis, Electrochemistry, and Photoinduced Processes

“…The Cu I -complexed rotaxane Si-C 60 -Cu with its two fullerene stoppers is reasonably soluble in CS 2 , CH 2 Cl 2 and CHCl 3 . In the 13 C NMR spectrum (CS 2 /CDCl 3 , 1:1) a total of 49 out of the 51 expected resonances for the C 2v -symmetric compound Si-C 60 -Cu (31 for the fullerene sp 2 carbons and 20 for the two diphenylphenanthroline fragments) are distinguishable in the aromatic and fullerene region and all 15 alkynyl and aliphatic signals are observed. The 1 H NMR spectrum is also in full accordance with the structure of Si-C 60 -Cu.…”

“…[11c±e] iv) sensitization of singlet oxygen [12] with unitary efficiency; [13] and v) a strong-electron acceptor character, as indicated by the presence of four to six fully reversible reduction processes [14] depending on the solvent. Accordingly, many investigations have been carried out on ground-state charge-transfer complexes and photoinduced electron transfer between C 60 and a variety of electron donors, including amines [15] and polymer substrates.…”