A new, versatile methodology for functionalization of single-walled carbon nanotubes (SWNTs), using 1,3-dipolar cycloaddition of nitrile imines to the sidewalls of SWNTs has been used to synthesize two soluble, photoactive single walled carbon nanotubes containing n-pentyl esters at the tips and 2,5-diarylpyrazoline units at the walls of the tubes. The success of the synthesis has been demonstrated by solution 1H and 19F NMR as well as UV−vis and FT-IR spectroscopy. These two compounds have been selected to have soluble single wall carbon nanotubes substituted either with an electron-poor 3,5-bis(trifluoromethyl)phenyl or electron-rich 4-(N,N-dimethylamino)phenyl on the C atom of the pyrazoline ring. Laser flash photolysis in dynamic flow of these carbon nanotubes in acetonitrile reveals the formation of several transient species decaying in the microsecond time scale. All the available data, including the photochemistry of model compounds, quenching experiments with electron donors and acceptors, and influence of acids, are compatible with the occurrence of an electron transfer from the electron rich substituents of the pyrazoline unit to electron acceptor termini including electron poor aryl rings and nanotube walls.