Synthesis, photochemistry, and electrochemistry of single-wall carbon nanotubes with pendent pyridyl groups and of their metal complexes with zinc porphyrin. Comparison with pyridyl-bearing fullerenes

A soluble, functionalized Py-SWNT has been synthesized and characterized by solution H-1 and C-13 NMR, FT-Raman, and electron microscopy. Experimental data indicate that Py-SWNT has short tubes with pentyl esters at the tips and pyridyl isoxazolino units along the walls. The synthesis of Py- SWNT is based on a 1,3-dipolar cycloaddition of a nitrile oxide on the SWNT walls, similar to 1,3- dipolar cycloadditions that are common for fullerene functionalization. The resulting Py-SWNT forms a complex with a zinc porphyrin (ZnPor) in a way similar to that reported for pyridyl-functionalized [60]-fullerenes. Formation of this metal-ligand complex was firmly established by a detailed electrochemical study. However, in contrast to the behavior observed for the ZnPor/ Py-C-60 complex, photochemical excitation of the complex between ZnPor/Py-SWNT does not lead to electron transfer with the generation of charge-separated states. Fluorescence and laser flash studies indicate that the main process is energy transfer from the singlet ZnPor excited state to the Py-SWNT with observation of emission from Py-SWNT. Triplet ZnPor excited-state quenching by Py-SWNT is only observed in polar solvents such as DMF, but not in benzonitrile.