Fluorochromic polymer films containing ultrasmall silver nanoclusters.

Fluorochromic materials that change their emission properties in response to their environment are of interest for the development of sensors, optical data storage and light-emitting materials. A thermally fluorochromic elastic polymer film that exhibits remarkable fluorochromism (from red to yellow) and enhancement of fluorescence intensity after thermal treatment (>120 °C) is designed by the incorporation of silver nanoclusters. The thermal treatment also leads to a significant increase of quantum yield and fluorescence lifetime. It is found that the thermo-induced etching on larger silver nanoclusters generates smaller silver nanoclusters. This simple and efficient size-tuning process in solid state is responsible for the thermo-fluorochromism and enhancement of fluorescence emission from silver nanoclusters. Such a thermo-fluorochromic polymer material is finally demonstrated to be useful for thermo-printing. This material illustrates a new way to make smart optical materials, particularly for potential applications in optical data storage and soft OLED display.