Photodynamics of a Constrained Parachute-Shaped Fullerene−Porphyrin Dyad

The pronounced ability of fullerene C{sub 60} to act as an electron and energy acceptor has led to the synthesis of a large number of compounds in which C{sub 60} is covalently linked to photoactivatable groups which can serve as potential donors. Such compounds are of interest as model systems for photosynthetic reaction centers and also have potential applications in photodynamic therapy because of the highly efficient photosensitization of singlet molecular oxygen formation by C{sub 60} and C{sub 60} derivatives. By far the largest number of such systems studied to date utilize porphyrins as antennas for efficient light capture in the visible region of the spectrum, and a variety of linkers. Photophysical studies as well as molecular modeling indicate that in conformationally flexible dyads the porphyrin (P) and C{sub 60} moieties are in close proximity, due to {pi}-stacking interactions, thus facilitating through-space interactions, as demonstrated by quenching of {sup 1}P{asterisk} fluorescence and generation of fullerene-excited states (by energy transfer) or P{sup +{sm{underscore}bullet}}-C{sub 60}{sup {minus}{sm{underscore}bullet}} ion-pair states (by electron transfer).