Advanced Functional Materials

Cover image for Vol. 25 Issue 20

17_10/2007Cover Picture: Covalent Functionalization of Carbon Nanohorns with Porphyrins: Nanohybrid Formation and Photoinduced Electron and Energy Transfer (Adv. Funct. Mater. 10/2007)

A transmission electron microscopy image of the spherical superstructure of dahlia flowerlike carbon nanohorns (CNHs), functionalized at the conical tips with porphyrins (H2P), is shown, together with an illustration of the architecture of the novel CNH–H2P nanohybrid material. Nikos Tagmatarchis, Osamu Ito, and co-workers report on the preparation and photophysical properties of this material on p. 1705. Photo-excitation of H2P with visible light results in reduction of the CNHs with a simultaneous oxidation of the porphyrin moiety, resulting in a charge-separated state; CNH–H2P+.

The covalent attachment of carbon nanohorns (CNHs) to &agr;-5-(2-aminophenyl)-&agr;-15-(2-nitrophenyl)-10,20-bis(2,4,6-trimethyl-phenyl)-porphyrin (H2P) via an amide bond is accomplished. The resulting CNH–H2P nanohybrids form a stable inklike solution. High-resolution transmission electron microscopy (HRTEM) images demonstrate that the original dahlia-flowerlike superstructure of the CNHs is preserved in the CNH–H2P nanohybrids. Steady-state and time-resolved fluorescence studies show efficient quenching of the excited singlet state of H2P, suggesting that both electron and energy transfer occur from the singlet excited state of H2P to CNHs, depending on the polarity of the solvent. In the case of electron transfer, photoexcitation of H2P results in the reduction of the nanohorns and the simultaneous oxidation of the porphyrin unit. The formation of a charge-separated state, CNH–H2P+, has been corroborated with the help of an electron mediator, hexyl-viologen dication (HV2+), in polar solvents. Moreover, the charge-separated CNH–H2P+ states have been identified by transient absorption spectroscopy.

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