Photochromic fluorophores at the molecular and nanoparticle levels: fundamentals and applications of diarylethenes

Fluorescent molecules and materials are widely used in many areas in physics, chemistry, and biology as emitters, tags, or sensors. The possibility of controlling their fluorescence signal by light, namely, fluorescence photoswitching, down to the nanoscale level can then dramatically extend their fields of applications. This review focuses on fluorescent and photochromic diarylethene-based nanosystems. The choice of the diarylethene family has been driven by its excellent photoswitching properties (conversion yield, bistability, fatigue resistance), which make them fully appropriate when high-performance behavior is required. The different molecular and nanomaterial designs providing suitable combinations of fluorescence and photochromism are summarized. Besides the inherently fluorescent diarylethene molecules, chemical association between photochromic and fluorescent molecular units can advantageously lead to fluorescence photoswitching thanks to resonance energy transfer or intramolecular electron transfer processes. Furthermore, the preparation of nanoscale emissive materials involving diarylethene units paves the way to new interesting features, such as near-infrared control of emissive and photoswitchable nanohybrids, giant amplification of the fluorescence photoswitching in organic nanoparticles, or fluorescence color modulation. Many applications derived from such fluorescent diarylethene-based molecules and nanomaterials have been developed recently, especially in the field of biology for fluorescence biolabeling and super-resolution imaging but also for photocontrol of biological functions. Extremely promising prospects are expected in the near future.