α-Cyanostilbene based fluorophores: Aggregation-induced enhanced emission, solvatochromism and the pH effect

A series of α-cyanostilbenes substituted with dimethylaniline, diphenylaniline and carbazole was synthesized and their optical spectroscopic properties in homogeneous solvents, the dioxane-water binary mixture and the solid state were investigated. Stilbenes (1 and 4) exhibit weak emission behavior in homogeneous solvents but show remarkable red-shifted emission along with enhanced intensity in water and in the solid state. This phenomenon is due to the aggregation induced enhanced emission effect. Other stilbenes also exhibit significant solvatochromic emission behavior and have similar enhanced emission characteristics in water and the solid-state. The sensitivity of emission to changes in acidic or basic strength establishes the utility of these molecules as fluorescence probes.