Evaluation of Proto- and Metallofluorochromism Effects in Enamine Switches

The fluorochromism effects of a series of enaminitrile switches have been explored in response to protons or transition metal ions. Switches based on a 2-pyridylacetonitrile group, linked to different aromatic entities via an enamine entity, were evaluated under acidic conditions or in the presence of Fe²⁺, Fe³⁺, Cu⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺ or Tb³⁺. Two different absorptive/emissive patterns were found, attributed to charge transfer (CT) or chelation-enhanced fluorescence (CHEF) effects, where selective metallofluorochromism could be recorded for Cu²⁺ and Zn²⁺ depending on the structures. The study provides comprehensive insights into how small structural modifications influence the responsive luminescence properties, and highlights the roles of transition metals in molecular communication.