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

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 (H 2 P) via an amide bond is accomplished. The resulting CNH–H 2 P 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–H 2 P nanohybrids. Steady‐state and time‐resolved fluorescence studies show efficient quenching of the excited singlet state of H 2 P, suggesting that both electron and energy transfer occur from the singlet excited state of H 2 P to CNHs, depending on the polarity of the solvent. In the case of electron transfer, photoexcitation of H 2 P results in the reduction of the nanohorns and the simultaneous oxidation of the porphyrin unit. The formation of a charge‐separated state, CNH • – –H 2 P • + , has been corroborated with the help of an electron mediator, hexyl‐viologen dication (HV 2+ ), in polar solvents. Moreover, the charge‐separated CNH • – –H 2 P • + states have been identified by transient absorption spectroscopy.