Carbon Nanohorn–Porphyrin Dimer Hybrid Material for Enhancing Light-Energy Conversion

The covalent grafting through a rigid ester bond of a dimeric porphyrin [(H2P)2] and carbon nanohorns (CNHs) was accomplished. The newly formed CNH–(H2P)2 hybrid was found to be soluble or dispersible in several organic solvents. Application of diverse spectroscopic techniques verified the successful formation of the CNH–(H2P)2 hybrid material. In addition, thermogravimetric analysis revealed the amount of (H2P)2 loading onto CNHs, and TEM studies showed the characteristic secondary spherical superstructure morphology of the hybrid material. Efficient fluorescence quenching of (H2P)2 in the CNH–(H2P)2 hybrid suggests that photoinduced events occur from the photoexcited (H2P)2 to CNHs. Nanosecond transient absorption spectroscopy revealed the formation of transient species such as (H2P)2•+ and CNH•– by photoinduced charge separation in CNH–(H2P)2. Additional proof for the photoinduced charge-separated state CNH•––(H2P)2•+ was obtained, from which the electron mediates to added hexyl viologen dication (HV2+). Finally, the CNH–(H2P)2 was adsorbed on nanostructured SnO2 electrode, to construct a photoactive electrode, which reveals photocurrent and photovoltage responses with an incident photon-to-current conversion efficiency value as large as 9.6%, without the application of any bias voltage.