Ultrafast relaxation dynamics of photoexcitations in fullerenes

We have studied relaxation dynamics of photoexcitations of C-60 and C-70 molecules in solution and in solid by means of a femtosecond pump and probe spectroscopy. Comparing the results for both C-60 and C-70, we discuss especially relaxation processes in C-70. With the excitation of the dipole allowed transition at 3 eV, the photoexcitations of C-70 molecules in solution are relaxed into the triplet state in similar to 1 ns. For C-70 solid, however, the fast relaxation occurs in 1.2 ps, which is interpreted in terms of the self-trapping of charge-transfer (CT) excitons.