Functionalization of diameter-sorted semiconductive SWCNTs with photosensitizing porphyrins: syntheses and photoinduced electron transfer

Abstract

Covalent functionalization of diameter sorted SWCNTs with porphyrins (MP), and photochemistry to establish nanotube diameter-dependent charge separation efficiencies are reported. The MP-SWCNT(n, m) [M = 2H or Zn, and (n, m)=(7,6) or (6,5)] nanohybrids are characterized by a variety of spectroscopic, thermogravimetric, TEM imaging techniques, and also by DFT MO calculations. The thermogravimetric, Raman and fluorescence studies reveal the presence of a moderate number of porphyrins on the SWCNT surface. The MO results suggest charge separation (CS) via the excited state of MP. Time-resolved fluorescence studies reveal quenching of the singlet excited state of the MP with SWCNT(n, m), giving the rate constants of charge separation (k(CS)) in the range of (4-5) x 10(9) s(-1). Nanosecond transient absorption measurements confirm the charge-separated radical cation and the radical anion as [MPC center dot+ -SWCNT center dot-] with their characteristic absorption bands in the visible and near-IR regions. The charge separated states persist for about 70-100 ns thus giving an opportunity to utilize them to build photoelectrochemical cells, which allowed us to derive the structure-reactivity relationship between the nature of porphyrin and diameter of the employed nanotubes.