Covalent Functionalization of Carbon Nanohorns with Porphyrins: Nanohybrid Formation and Photoinduced Electron and Energy Transfer

Abstract The covalent attachment of carbon nanohorns (CNHs) to α‐5‐(2‐aminophenyl)‐α‐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.