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 center dot+ was accumulated in the polar organic solvent. This observation suggests that photoinduced charge-separation takes place, producing CNH center dot- - pyrene(center dot+), which was further confirmed by observing pyrene(center dot+) in the nanosecond time-scale transient absorption spectra. From CNH center dot-, an electron is migrated to HV2+ and a hole shifts from pyrene(center dot+) to the hole trap, which suppresses the back electron transfer resulting in the persistence of HV center dot+.