β-Cyclodextrin Encapsulated Coumarin 6 on Graphene Oxide Nanosheets: Impact on Ground-State Electron Transfer and Excited-State Energy Transfer.

We report a unique phenomenon of physical adsorption of coumarin 6-β-cyclodextrin (C6-β-CD) inclusion nanostructures on graphene oxide (GO) nanosheets, thus inducing ground-state electron transfer from the C6-β-CD composite to GO. On excitation, the C6-β-CD composite initially transfers energy to the attached GO surface and subsequently collides with similar C6-β-CD@GO adducts leading to dynamic quenching of energy. The ground-state two-electron transfer process has been confirmed by cyclic voltammetry in aqueous medium, whereas the excited-state processes were inferred from steady-state and time-resolved fluorescence spectroscopy. The concept is developed toward conceiving control over the ground-state electron transfer and excited state energy transfer from the C6-β-CD composite by the adsorbed electron accepting medium (GO in this case). The C6-β-CD composite has been prepared to isolate single C6 molecules that readily undergo microcrystal formation in aqueous medium. The results show its potential toward fabrication of energy-harvesting antenna for further applications.