Covalent functionalization of single-walled carbon nanotubes using meso-tetra(4-aminophenyl) porphyrin and its zinc complex

Abstract

Covalent linking of 5,10,15,20 meso tetra(4-aminophenyl) porphyrin (TAP) and its zinc complex with single-walled carbon nanotubes (SWCNTs) (nanohybrids A and B, respectively) has been reported. Significant decrease in the intensity of D-band and higher frequency shift of G-band of SWCNT-TAP in Raman spectrum reveals the improved graphitic sp2 hybridization of SWCNT as compared to SWCNT-ZnTAP. This is due to the functionalization of free base porphyrin (electron donating group) in the nanohybrid A. Shifting of carbonyl stretching frequency from 1700 cm−1 to 1680 cm−1 and further appearance of striking bands in the X-ray photoelectron spectroscopy (XPS) and FTIR spectra of nanohybrids A and B confirm the covalent linking of porphyrin chromophores with SWCNTs. XPS reveals that the extent of functionalization of nanohybrid A is more as compared to nanohybrid B. These nanohybrids demonstrate positive solvatochromism. Upon excitation at 450 nm, the nanohybrids A and B reveal ∼76% and 65% fluorescent quenching of emission bands at 686 and 632 nm, respectively. This is due to the energy or electron transfer from porphyrins to SWCNTs.