Aggregation‐Induced Emission of 4‐Dicyanomethylene‐2,6‐Distyryl‐4<i>H</i>‐pyran

Abstract A new pyran ( 1 ) is synthesized. When molecularly dissolved in acetone, 1 is practically nonemissive. Addition of water induces it to cluster into nanoaggregates, which turns its emission “on” and boosts its luminescence efficiency dramatically. The color of its emission changes from green to red upon aggregation.