Water-soluble cruciforms and distyrylbenzenes: synthesis, characterization, and pH-dependent amine-sensing properties

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.