Donor−Acceptor Nanohybrids of Zinc Naphthalocyanine or Zinc Porphyrin Noncovalently Linked to Single-Wall Carbon Nanotubes for Photoinduced Electron Transfer

Abstract

The occurrence of photoinduced electron transfer in donor−acceptor self-assembled zinc naphthalocyanine (ZnNc) or zinc porphyrin (ZnP) single-wall carbon nanotube (SWNT) nanohybrids has been demonstrated. The nanohybrids were constructed by solubilizing carbon nanotubes by π−π stacking of pyrene functionalized to bear an imidazole moiety, ImPy-SWNT. Through the use of the imidazole ligand of the soluble ImPy-SWNT, donor ZnNc and ZnP entities were axially coordinated to yield ZnNc−ImPy-SWNT and ZnP−ImPy-SWNT donor−acceptor nanohybrids. The nanohybrids thus obtained were fully characterized by using transmission electron microscopy, UV−visible-near infrared spectroscopy, and electrochemical methods. Steady-state and time-resolved emission studies revealed efficient fluorescence quenching of the donor, ZnP, and ZnNc entities in the nanohybrids. Nanosecond transient absorption spectra revealed that the photoexcitation of the ZnNc or ZnP moiety resulted in the one-electron oxidation of the donor unit with a simultaneous one-electron reduction of SWNT. The charge separation yielding ZnNc•+−ImPy-SWNT•- and ZnP•+−ImPy-SWNT•- was further confirmed with the aid of an electron mediator, hexyl-viologen dication (HV2+) and an electron-hole shifter, 1-benzyl-1,4-dihydronicotinamide. As a result of the photoinduced processes, accumulation of the radical cation of HV•+ was observed with 70−90% yields thus demonstrating the importance of the present donor−acceptor nanohybrids in photogeneration of redox products.