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.

Keywords:

• Carbon nanotubes
• chromophores
• fluorescent quenching
• metalloporphyrin
• photo-luminescent
• solvatochromism

Acknowledgements

We acknowledge COE-AMGT centre (MHRD, New Delhi) for the instrumental facility. We also thank Mr. S. Sarath, ACNSMM, AIMS Kochi for recording XPS.

Disclosure statement

There are no conflicts of interest to declare.

Additional information

Funding

This study was supported by Ministry of Human Resource Development, Fast Scheme.