Anion Radicals of Mono- and Bisfulleropyrrolidines:  g Tensors, Spin Density Distribution and Spin−Lattice Relaxation

Abstract

The radical anions of two C60 Nteg-fulleropyrrolidine (teg = 3,6,9-trioxadecyl) adducts, the monoadduct and the trans1-bisadduct have been studied in liquid solution and glassy matrix of 2-MeTHF by continuous wave (cw) and pulsed X-band EPR and cw high-frequency EPR. The hyperfine coupling constants of the 14N nuclei and of the 13C nuclei in natural abundance have been determined and discussed, also in relation with the spin density distribution on the fullerene sphere obtained by restricted Hartree−Fock half-electron approximation (RHF-HE), and the hyperfine coupling constants obtained with the density functional method. The calculation results show a reasonable agreement with the experimental data. The g tensors have been determined by HF-EPR in frozen matrix at low temperature, the monoadduct showing a rhombic tensor and the bisadduct an axial one. The temperature dependence of the EPR line widths and of the electron spin−lattice relaxation times measured by Inversion Recovery of the magnetization have been studied. The radical anion of the bisadduct shows line widths decreasing on increasing the temperature, as usually expected, whereas the radical anion of the monoadduct shows the opposite behavior. The electron spin−lattice relaxation times at room temperature are respectively T 1 = 2.8 μs and T 1 = 200 ns. The relaxation behavior has been discussed and compared with that of the C60 monoanion and of other fulleropyrrolidine adducts, taking into account the time modulation of the parameters of the spin Hamiltonian due to the reorientation in solution, and the coupling between rotational and electron spin magnetic moments. This spin-rotational mechanism gives rise to the short T 1 and anomalous temperature dependence of the line widths in the monoadduct, whereas the larger stiffness of the bisadduct reduces this effect.

Synthesis, Photophysics, and Photoresponse of Fullerene‐Based Azoaromatic Dyads

“…The narrow line g factor (g = 2.0005 AE 0.0005) could be reasonably attributed to the fullerene radical anion. [39] This demonstrates that an electron transfer takes place after light excitation, and that the charge-separated state is sufficiently long-lived (about 1 ms) to be detected. On the other hand, for dyads 2 b-4 b the line in absorption is missing (or extremely weak), indicating the absence of a long-lived charge-separated state.…”

Radical reactions of C60Ph5Cl: EPR study and DFT calculations

“…Because of the size of the molecules, we used semi-empirical molecular orbital theory to optimize the geometry, as it was done in the study of Å C 70 H [5] and radicalanions of mono-and bis-(trans-1-fulleropyrrolidines) [14]. The calculations were done with the MNDO Hamiltonian with the PM3 parametrization at the ROHF level.…”

“…In previous studies of hfc constants and density distributions in fullerenes and their derivatives, other authors [5,11,14] used both semi-empirical and DFT methods. For studying of the products of the reaction of Å OH with watersoluble C 60 [C(COOH) 2 ] n (n ¼ 2-6) the authors used semi-empirical molecular orbital (AM1 and PM3) calculations and Huckel molecular orbital theory [11].…”

ENDOR Evidence of Electron–H2Interaction in a Fulleride Embedding H2

“…For example, the 13 C T 1 of the carbon cage is not affected by the presence of the endo H 2 . 8 Similarly, the interactions of incarcerated H 2 and D 2 with the excited triplet of fullerene 3 C 60 were found to be too weak to be measured by either triplet lifetime measurements (triplet− triplet absorption) or time-resolved EPR spectroscopy.…”

“…13 CW-EPR spectra of both fullerides were acquired in the temperature range from 290 to 80 K, carefully adjusting the radical concentration in order to minimize the line width of the EPR signal. The H 2 @NMP and NMP monoanion spectra appear very similar in this temperature range and exhibit the well-known features attributable to the hyperfine coupling with the pyrrolidinic nitrogen (three lines in the ratio 1:1:1) and smaller lines on the wings due to 13 C couplings. 14 No further splitting attributable to coupling with ortho-H 2 is observable in the H 2 @NMP monoanion spectra, even in the liquid solution at 160 K, where the line width is the narrowest, although there may be additional broadening of the H 2 @NMP peaks.…”