ULTRAFAST RELAXATION OF EXCITONS AND PHOTOPOLYMERIZATION IN C-60 AND C-70

We have studied relaxation dynamics of photoexcitation in C-60 and C-7 0 molecules and solids by means of a femtosecond pump and probe spectr oscopy. With the excitation of the dipole allowed transition at 3 eV, the photoexcitations in C-60 solution relax into the triplet state in 900 ps. For solid C-60, however, the fast relaxation occurs in 1 ps, w hich is interpreted in terms of the self-trapping of charge-transfer ( CT) excitons in the simple cubic lattice. Such a self-trapped CT excit on seems to be a precursor to the photopolymerization. A similar dynam ical behavior has been observed for solid C-70.