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The development of fluorescent Cd²⁺ sensors requires strict selectivity over Zn²⁺ because of the high availability of Zn²⁺ in the natural environment. In this paper, bisquinoline-based fluorescent sensors with a 2-aminoethanol backbone were investigated. The weak coordination ability of quinoline compared to well-studied pyridine is suitable for Cd²⁺ selectivity rather than Zn²⁺. In the presence of 3 equiv. of metal ions, TriMeO-<i>N,O</i>-BQMAE (<i>N,O</i>-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methylaminoethanol (<b>3</b>)), as well as its <i>N,N</i>-isomer TriMeO-<i>N,N</i>-BQMAE (<i>N,N</i>-bis(5,6,7-trimethoxy-2-quinolylmethyl)-2-methoxyethylamine (<b>6</b>)), exhibits Cd²⁺-selective fluorescence enhancement over Zn²⁺ in DMF-HEPES buffer (1:1, 50 mM HEPES, 0.1 M KCl, pH = 7.5) (<i>I</i>_Zn/<i>I</i>_Cd = 26–34%), which has similar selectivity in comparison to the corresponding ethylenediamine derivative TriMeOBQDMEN (<i>N,N’</i>-bis(5,6,7-trimethoxy-2-quinolylmethyl)-<i>N,N’</i>-dimethylethylenediamine) under the same experimental condition (<i>I</i>_Zn/<i>I</i>_Cd = 24%). The fluorescence mechanisms of <i>N,O</i>- and <i>N,N</i>-isomers of BQMAE are quite different, judging from the fluorescence lifetimes of their metal complexes. The Cd²⁺ complex with TriMeO-<i>N,O</i>-BQMAE (<b>3</b>) exhibits a long fluorescence lifetime similar to that of TriMeOBQDMEN via intramolecular excimer emission, whereas the Cd²⁺ complex with TriMeO-<i>N,N</i>-BQMAE (<b>6</b>) exhibits a short lifetime from monomer emission.