Hydroxycruciforms: Amine-Responsive Fluorophores

The synthesis of three hydroxy‐substituted cruciforms (XF, 1,4‐bis(4′‐hydroxystyryl)‐2,5‐bis(4′′‐methoxyphenylethynyl)benzene, 1,4‐bis(4′‐methoxystyryl)‐2,5‐bis(4′′‐hydroxyphenylethynyl)benzene, and 1,4‐bis(4′‐hydroxystyryl)‐2,5‐bis(4′′‐hydroxyphenylethynyl)benzene) starts with a Horner reaction followed by a Sonogashira coupling and subsequent deprotection. The three herein described XFs contain either two or four free phenolic hydroxyl groups. All three XFs were subjected to photometric UV/Vis titrations in a methanol/water mixture. The respective pKa values were obtained by data deconvolution. As the three XFs display a significant change in emission color upon photoinduced deprotonation, the XFs were taken up in different solvents and exposed to twelve amines. The amine‐dependent change in emissivity of the tetrahydroxy XF is sufficiently distinct in the eight solvents that all of the inspected amines are discerned by a linear discriminant analysis. The tetrahydroxy XF in different solvents forms a sensor array, the response of which is based on the excited‐state proton transfer (ESPT) to amines and mediated by the choice of the battery of solvents that are utilized. Amine detection made easy: One fluorophore in eight different solvents (columns in graphic) allows the unambiguous identification of twelve different amines (along one row) based on the distinct fluorescence changes through excited‐state proton transfer.