The potentially hexadentate ligand L, which contains two terminal coumarin fluorophores, forms dinuclear double-stranded helicates with dicationic metal ions, giving species of the generic form [M2L2]4+. In solution the free ligand was fluorescent with emission attributed to the coumarin fluorophores (λem = 437 nm). The luminescent properties of the corresponding dimetallic helicates complexes were examined and revealed that the Zn2+ complex demonstrates enhanced emission when compared to the parent ligand, whereas Co2+, Cu2+, Cd2+ and Hg2+ induce varying degrees of fluorescence quenching. In particular, comparative luminescence measurements at 77 K and room temperature showed that the quenching mechanism for [Cu2L2]4+ can be attributed to a photoinduced electron transfer. ESI-MS selectivity studies showed that in the presence of a mixture of metal dications no preference for any one metal ion was observed.
Bullock, S. J., Felton, C. E., Fennessy, R. V., Harding, L. P., Andrews, M., Pope, S. J. A., Rice, C. R., & Riis-Johannessen, T. (2009). Coumarin-based luminescent ligand that forms helicates with dicationic metal ions. Dalton Transactions, (47), 10570-10573. https://doi.org/10.1039/B913103E