Fullerene-coumarin dyad as a selective metal receptor: synthesis, photophysical properties, electrochemistry and ion binding studies.

A coumarin derivative with a malonate unit has been synthesized and used for the preparation of a fullerene-coumarin dyad through the Bingel cyclopropanation method. The newly synthesized dyad is soluble in organic solvents and has been fully characterized with traditional spectroscopic techniques. Electronic interactions between the two components of the dyad were probed with the aid of UV/Vis spectroscopy, fluorescence emission, and electrochemistry measurements. Our studies clearly show the presence of electronic interactions between C(60) and modified coumarin in the ground state; efficient electron-transfer quenching of the singlet excited state of the coumarin moiety by the appended fullerene sphere was also observed. Time-resolved fluorescence measurements revealed lifetimes for the coumarin-C(60) dyad at a maximum of 50 ps, while the quantum yield was reaching unity. Additionally, the redox potentials of the C(60)-coumarin dyad were determined and the energetics of the electron-transfer processes were evaluated. Finally, after alkaline treatment of C(60)-coumarin, which resulted in the deprotection of carboxylate units, the dyad was tested as a metal receptor for divalent metal cations; ion competition studies and fluorescence experiments showed binding selectivity for lead ions.