Photoinduced electron-transfer processes of carbon nanohorns with covalently linked pyrene chromophores: Charge-separation and electron-migration systems

Carbon nanohorns (CNHs) have been covalently functionalized with pyrene chromophores forming dispersible nanohybrids in CH₂Cl₂. Their photo-physical properties have been investigated by complementary steady-state and time-resolved absorption and fluorescence spectroscopies as well as electrochemistry. Upon photo-excitation of CNH-pyrene nanohybrids, in the presence of hexyl-viologen dication (HV²⁺) and a hole trap, the HV⁺ was accumulated in the polar organic solvent. This observation suggests that photoinduced charge-separation takes place, producing CNH ^--pyrene⁺, which was further confirmed by observing pyrene⁺ in the nanosecond time-scale transient absorption spectra. From CNH^-, an electron is migrated to HV²⁺ and a hole shifts from pyrene⁺ to the hole trap, which suppresses the back electron transfer resulting in the persistence of HV⁺.