Syntheses and Optical Limiting Characterizations of a Series of Porphyrin-Buckminsterfullerene Dyads

We report herein the syntheses and optical limiting characterizations of a series of porphyrin-C60 dyads in which the porphyrin and C60 moieties are held within close proximity of one another by an o-phenylene bridge. The electron-donating ability of the porphyrin moiety in the dyads is systematically varied through chemical modification. This allows us to control the ease of electron transfer from the porphyrin to the C60 moiety in these dyads. Optical limiting measurements at 532 nm using 3-ns pulses show that the limiting performances of the dyads are poorer relative to their model compounds. This could be due to an ultra-short lifetime for the charge-separated species or a depopulation of the triplet states by photoinduced electron transfer. The optical limiting performances of the free-base porphyrin-C60 dyads are also related to the electron- donating abilities of the meso substituents of the porphyrin moieties. 12PorphyC60 displays better limiting performance at 532 nm (with 3-ns and 15-ns pulses) compared to Val12PorphyC60. This trend has been rationalized in terms of the relative energies of the first excited singlet and triplet states of the fullerene moiety and the charge-separated state of the dyads.