(Terpyridine)copper(II)-carbon nanohorns: Metallo-nanocomplexes for photoinduced charge separation

New metallo-nanostructured materials of carbon nanohorns (CNHs), within the family of elongated carbon nanotubes, have been prepared by the coordination of copper(II)-2,2':6',2 ''-terpyridine (Cu(II)tpy) with oxidized carbon nanohorns (CNHs-COOH). The resulted CNHs-COO-Cu(II)tpy metallo-nanocomplexes have been characterized by diverse analytical spectroscopic tools and cyclic and differential pulse voltammetry. Scanning transmission electron microscopy (STEM), dynamic light scattering (DLS), and energy dispersive X-ray spectroscopy (EDX) measurements have been employed to probe the morphological characteristics and particle-size distribution of CNHs-COO-Cu(II)tpy as well as to investigate the elemental composition of the metallo-nanocomplex. Steady-state and time-resolved fluorescence emission studies have shown efficient fluorescence quenching, suggesting that electron transfer occurs from the singlet excited state of Cu(II)tpy to CNHs. Photoexcitation of Cu(II)tpy resulted in the one-electron reduction of nanohorns with a simultaneous one-electron oxidation of the Cu(II)tpy unit (CNHs(center dot-)-COO-(Cu(II)tpy)(center dot+)) as revealed by transient absorption measurements. The charge-separated state of CNHs(center dot-)-COO-(Cu(II)tpy)(center dot+) has been confirmed with the aid of an electron mediator, such as hexyl-viologen dication (HV2+) and an electron-hole shifter in polar solvents.