Unlocking Light-Up Effect of Push–Pull Hemicyanine Dyes in Hybrid Silicate Dispersions: Impact of the Terminal Arylamine Functionality and Intermolecular Surface Distances

Emission enhancement of cationic dipolar hemicyanines was observed upon their adsorption onto the layered silicate saponite. The extent of the light-up effect depends on the type of the terminal arylamine group and the concentration on the silicate surface. Dye-structure modification included gradual rigidification of the triarylamine moiety in the molecules, progressing from the nonplanar, propeller-shaped triphenylamine via the semirigidified carbazole to the fully rigidified azatriangulene. In addition, we explored the photoluminescence properties of corresponding cyanine dyes with planar, sterically less demanding <i>N</i>,<i>N</i>-dialkylaminoaryl groups, which, unlike derivatives with the triarylamine moiety, preferentially formed dye aggregates even at low concentrations. The resulting spectral properties were attributed to a combination of surface fixation-induced emission, concentration quenching, aggregation-caused quenching, and aggregation-induced emission. These phenomena existed in dynamic equilibrium, and their impact was influenced by the structure of the terminal arylamine group.