Spin Dynamics of C60 Triplets

Abstract

A study of the photoexcited triplet state of Cm (3C,5,9 in liquid solution (toluene, methylcyclohexane) was made using pulsed-EPR techniques. The spin-lattice relaxation time ( T I ) , phase-memory time ( T m ) , and line width (Av1p) were measured as function of temperature (1 70-360 K). The results were used to analyze Some aspects of the spin dynamics of 3Cm. The data confirm earlier findings that therelaxation toward Boltzmannequilibrium is responsible for the initial growth of the signal amplitude when FT-EPR spectra are measured as a function of delay time between laser excitation and 7r/2 microwave pulse. Also, it is found that A q p -l/aTm in both solvents over the whole temperature range. This establishes that there is a negligible contribution to the line width from unresolved I3C hyperfine structure. The contribution of the electron spin-spin interaction modulated by rotational motion to the relaxation rates is analyzed. The analysis shows that the value of the zero-field splitting parameter D, which determines the magnitude of this contribution, is about an order of magnitude less than that found in rigid matrices at low temperature. A significant residual, temperature-independent, relaxation contribution is found which may stem from the rapid interconversion between triplet states that causes the reduction in D upon going from solid state to liquid solution.

Recent Developments in Studies of Electronic Excited States by Means of Electron Paramagnetic Resonance Spectroscopy

“…In that sense C 60 is not sufficient. Although the analysis of ZFS has been made by Steren et al, 16 the one sharp peak signal did not provide reliable information on the electronic structure. Actually, 3 C 60 Ã is an exceptional case of ultra high symmetry,…”

The structure and electronic state of photoexcited fullerene linked with a nitroxide radical based on an analysis of a two-dimensional electron paramagnetic resonance nutation spectrum

“…D T , g R , A R , and g T stand for those of a noncoupled radical or a triplet state. We neglected hyperfine couplings due to 13 C atoms on 3 C 60 , because the magnitude was estimated to be less than 1 MHz ͑Ref. 15͒ in the excited quartet states.…”

“…1,2 It is shown, however, by an electron paramagnetic resonance ͑EPR͒ technique that C 60 distorts from the I h symmetry in the photoexcited triplet state via an observation of zero-field splittings ͑zfs͒. 3,4 Although the molecular structure and the electronic state of the excited triplet states of C 60 ( 3 C 60 ) have been extensively studied theoretically [5][6][7] and experimentally, 3,4,[8][9][10][11][12][13][14][15][16] a description of the structure and even the symmetry of 3 C 60 are still under the debate. On the basis of calculated energies and zfs of possible Jahn-Teller states having D 5d , D 3d , and D 2h symmetries, Surján et al predicted that the state of D 5d symmetry is a little more stable ͑2 meV͒ than that of D 2h symmetry.…”

Time resolved EPR of [70]fullerene monoadducts in the photoexcited triplet state

“…[2][3][4][5][6] The excited triplet state of [60]fullerene, and of a great number of its derivatives, has been extensively studied by EPR, ODMR and optical spectroscopies. [7][8][9][10][11][12] Information on the electron distribution and on the dynamic processes, such as dynamic Jahn-Teller distortion (in 3 [60]fullerene) and rotational diffusion in solution, was obtained. 13 A few investigations were also carried out on the triplet state of pristine [70]fullerene [14][15][16][17][18][19][20] but data are scarce for [70]fullerene adducts, even though several of them have been prepared.…”