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Characterisation of nanohybrids of porphyrins with metallic and semiconducting carbon nanotubes by electron paramagnetic resonance and optical spectroscopy

Single-walled Carbon Nanotubes (SW CNTs) are noncovalently functionalised with octaethylporphyrins (OEPs) and the resulting nanohybrids are isolated from the free OEPs. Electron paramagnetic resonance (EPR) spectroscopy of paramagnetic cobalt(II)OEP, adsorbed on the nanotube walls by  - -stacking, demonstrates that the CNTs act as electron acceptors and that the spin density located on the cobalt(II) ion is redistributed towards the CNTs when forming the nanohybrid. EPR is shown to be very effective in resolving the different interactions for metallic and semiconducting tubes. Water solubilisation of the porphyrin/CNT nanohybrids using bile salts, after applying a thorough washing procedure, yields solutions in which at least 99% of the porphyrins are interacting with the CNTs. Thanks to this purification, we observe, for the first time, the isolated absorption spectrum of the interacting porphyrins, which is strongly red shifted compared to the free porphyrin absorption. In addition also a quasi-complete quenching of the porphyrin fluorescence is observed.

nanohybrids ; nanotubes ; electron paramagnetic resonance

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