16 December 1996 Photophysical properties of functionalized fullerene derivatives: a selective overview
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Time-resolved and steady-state techniques are employed to explore the photophysical properties of C60C(COOEt)2, equatorial-C60[C(COOEt)2]2, trans3- C60[C(COOEt)2]2, trans2-C60[C(COOEt)2]2, and equatorial-C60[C(COOEt)2]3. Picosecond-resolved energy transfer to the fullerene core results in the formation of the excited singlet state with remarkably blue-shifted singlet-singlet transitions in going from C60 to 3. Rapid formation of the triplet-triplet absorption as a consequence of intersystem crossing to the energetically lower lying excited triplet state suffers a deceleration with increasing number of functionalizing addends. The corresponding triplet-triplet absorption energies also show a significant dependence on the degree and site of functionalization, spreading over a range of 100 nm. Energy transfer from radiolytically excited biphenyl to the fullerene's ground state, corroborates the photolytic data. 0->0 transitions from the lowest level of the excited singlet state and excited triplet state are mirror- images to the reversed 0->0 absorption transitions. Red- shifts of these emission, relative to pristine C60, again sensitively reflect the degree and site of functionalization. Cyclic voltammetry and reductive quenching of triplet excited fullerenes demonstrate that functionalization of the fullerene's (pi) -system obstructs the ease of reduction in the ground and excited triplet state. An increasing number of bis(ethoxycarbonyl)methylene groups shifts the redox potential of the ground state from -0.54 to -0.86 V versus SCE and of the excited triplet state from +1.01 V versus SCE to +0.64 V versus SCE for C60 and 3, respectively.
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Dirk M. Guldi, Klaus-Dieter Asmus, "Photophysical properties of functionalized fullerene derivatives: a selective overview", Proc. SPIE 2854, Fullerenes and Photonics III, (16 December 1996); doi: 10.1117/12.262984; https://doi.org/10.1117/12.262984

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