Facile Assembly Enhanced Spontaneous Fluorescent Response of Ag⁺ Ion Containing Polyelectrolyte Multilayer Films

Fluorescent organic-inorganic composite materials exhibiting "turn-on" response are often based on conjugated small molecules. Conjugated polymers, however, often exhibit a "turn-off" response in combination with metal ions. Here we present fluorescent turn-on behavior of a branched poly(ethylene imine)-poly(acrylic acid)-Ag⁺ ion complex in a thin film. The material is characterized by UV-vis, spectrofluorometry, XPS, and ICP-MS. The turn-on response is exhibited only with all three components present, implying that the optically active metal coordination complex contains amine and carboxylic acid groups. This behavior is observed in the solid state, meaning this material could be easily integrated into devices. We demonstrate sensing of formaldehyde vapor as well as halide containing solutions based on fluorescence quenching. This fluorescent material is simply made using the layer-by-layer technique and commercially available polymers.