Preparation and pH-Switching of Fluorescent Borylated Arylisoquinolines for Multilevel Molecular Logic

The preparation of pH-switchable fluorescent borylated arylisoquinoline dyes via a flexible iridium-catalyzed route is reported. The obtained dyes feature aromatic amino substitution and lateral aliphatic amino groups as electron donors. The photophysical properties of the internal charge transfer dyes were studied, which was complemented by density functional theory calculations. Appreciable fluorescence quantum yields (Phi(f) up to ca. 0.4) and characteristic spectral fingerprints in the green to red emission range were observed. The fluorescence modulation upon multiple and orthogonal protonation with triflic acid was studied and led to the interpretation of multilevel switching including off-on-off, ternary, and quaternary responses.