Noncovalent Binding between Fullerenes and Protonated Porphyrins in the Gas Phase

Noncovalent interactions between protonated porphyrin and fullerenes (C60 and C70) were studied with five different meso-substituted porphyrins in the gas phase. The protonated porphyrin−fullerene complexes were generated by electrospray ionization of the porphyrin−fullerene mixture in 3:1 dichloromethane/methanol containing formic acid. All singly protonated porphyrins formed the 1:1 complexes, whereas porphyrins doubly protonated on the porphine center yielded no complexes. The complex ion was mass-selected and then characterized by collision-induced dissociation with Xe. Collisional activation exclusively led to a loss of neutral fullerene, indicating noncovalent binding of fullerene to protonated porphyrin. In addition, the dissociation yield was measured as a function of collision energy, and the energy inducing 50% dissociation was determined as a measure of binding energy. Experimental results show that C70 binds to the protonated porphyrins more strongly than C60, and electron-donating substituent...