Pulsed-EPR on the photoexcited triplet state of C60

The photoexcited triplet state of C60 has been investigated by the pulsed EPR technique. A line shape analysis has been performed in order to determine the triplet spin dynamics in frozen and in liquid solutions. In frozen solution the EPR line shape reveals exchange narrowing which can be simulated rather well by assuming an exchange between the equivalent states of D5d symmetry of the lowest triplet state. The determined exchange rate turned out to be only weakly temperature dependent and suggests that the dynamics is due to tunneling between Jahn-Teller distorted states rather than to real molecular jumps. Measurements on a modified C60 molecule, where the high symmetry is reduced due to chemical substitution, support the above interpretation. In liquid solution the EPR signal of 3C60 could be identified by means of electron transfer reactions. The corresponding spin dynamics is analyzed.