NMR Studies into the Potential Interactions of Fullerene C[subscript]60, with Tetraphenylporphyrin, H[subscript]2[TPP] and Some of its Derivatives

Abstract

The curved [pi] surface of fullerene, C[subscript]60, shows a tendency to interact with other molecules, making it an interesting target for building supramolecular arrays. The interaction can be relative strong and may even exist in solutions, often leading to stable complexes. An important class of the macrocycles that interacts with fullerenes is the porphyrins. In our study, [superscript]1H NMR spectrometric studies have been done to gain information on the nature and the precise interaction site of fullerene 1, with tetraphenylporphyrin, H[subscript]2[TPP] 2, and para-substituted tetraphenylporphyrins, H[subscript]2[(p-X)[subscript]4TPP], where X= CN and OCH[subscript]3 in deuterated chlorobenzene-d[subscript]5(CBZ) and toluene-d[subscript]8. The porphyrin derivatives have been used to investigate any correlation in the interaction site due to changes in substituent. Relaxation rates of the pyrrole and phenyl hydrogen in the porphyrins were determined at temperatures of 288, 298 and 313 K for all the complexes in the presence and in the absence of fullerene, C[subscript]60. To study solvent effects on interactions, Toluene-d[subscript]8 and chlorobenzene-d[subscript]5 solvents were used. Overall, our data indicated that C[subscript]60 interacted with H[subscript]2[TPP] at both the pyrrole and phenyl hydrogen sites however, these intermolecular interaction are not long-lasting in chlorobenzene-d[subscript]5. The porphyrin derivatives showed that the substituents have an effect on which site is preferred for interaction. For the case of H[subscript]2[(p-OCH[subscript]3)[subscript]4TPP], that has an electron -donating group, both phenyl and pyrrole hydrogen sites interacted with C[subscript]60 , but preferably at the pyrrole hydrogen at all the three temperatures(283, 298, and 313 K). In the case of H[subscript]2[(p-CN)[subscript]4TPP] with an electron-withdrawing group CN, our data indicates that at lower temperature there is a noticeable, but slight preference for the interaction of C[subscript]60 at pyrrole site but is quickly destroyed with an increase in temperature.