Fluorescence sensing based on cation-induced conformational switching: copper-selective modulation of the photoinduced intramolecular charge transfer of a donor-acceptor biphenyl fluorophore |
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Authors: | John Cody |
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Institution: | School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, GA 30332, USA |
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Abstract: | The fluorescence emission energy of donor-acceptor substituted biphenyls is highly sensitive towards conformational changes of the interannular twist angle. By integrating 4-dimethylamino-4′-cyano-biphenyl into the ligand backbone of a thioether-rich metal receptor we designed a fluorescence sensor that exhibits high selectivity towards copper. Upon metal binding the ligand undergoes a significant conformational change, which induces a strong hypsochromic shift of the photoinduced charge-transfer emission. Steady-state absorption and fluorescence spectroscopy revealed a high affinity towards Cu(I) with a well-defined 1:1 metal-ligand complex stoichiometry. The nature of the conformational changes upon Cu(I) coordination were analyzed in detail by 1H NMR and 2D NOESY experiments. The spectroscopic data provide a coherent picture, which is consistent with a Boltzmann ground-state distribution of several rotamers that are locked into a more flattened geometry upon coordination of Cu(I). |
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Keywords: | Fluorescence sensor Copper Photoinduced charge transfer Ligand design Donor-acceptor fluorophores |
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