Three water-soluble fluorescent aldehyde-substituted distyrylbenzene derivatives were prepared using Heck or Horner methodologies. Water solubility was achieved through the addition of branched oligoethylene glycol side chains; these are attached via an ether bridge to the aromatic nucleus. The aldehydes are almost nonfluorescent in water, but addition of primary amines turns the fluorescence on; formation of imines results. Control of the basicity of the media allows further discrimination of the analytes employed. 1,3-Diaminopropane reacts with these aldehydes. Instead of an imine, a brightly fluorescent aminal forms. Amino acids are almost always nonreactive toward these aldehydes. Exceptions are lysine and cysteine, which form an imine and a thioaminal, respectively, discreating the aldehyde unit under fluorescence turn-on in water. The detection limit and time of completion of the sensing event were evaluated. Dialdehydes 3 and 16 were comparable on both counts. The cross-shaped 16 did react approximately twice as quickly with 1,3-diaminopropane.
We developed a series of new conjugated cruciform fluorophores (XF) featuring imine groups. The condensation of an XF containing aldehyde functionalities and selected primary amines leads to several XF-imine derivatives. Upon addition of Cu(2+) or Zn(2+) ions to solutions of the imine XFs in different solvents, a red-shifted emission is detected, resulting in an altered emission color. The imine acts as a simple modular metallo-reactive fluorophore.
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