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. Photosensitive chemicals that transform in response to light are helping researchers develop probes for both imaging and manipulating biomolecules. Tuyoshi Fukaminato from Kumamoto University in Japan and Rémi Métivier at France’s Université Paris-Saclay review efforts to produce color-changing compounds by combining fluorescent dyes with diarylethenes, stable organic molecules that can switch between open- and closed-ring shapes. Experiments showing that certain ring-closing reactions can paralyze worms demonstrate how biological events could be switched on at the same time as the probes are activated. Probes that light up after photo-transformations are becoming increasingly important in super-resolution images of single cells. Advanced composites, such as polymer nanoparticles that encapsulate the dyes and diarylethenes and keep them precisely separated, have provided multi-color internal views of small animals, including mice and zebrafish. Fluorescent diarylethenes are the most attractive molecules for several applications, such as optical memories, optical switches, or probes for the imaging technology. A wide variety of fluorescent diarylethenes combining with organic fluorophores, emissive polymers, or fluorescent inorganic materials have been developed from the molecular level to the nanoscale during the past decade. In this review, the different molecular and nanomaterial designs providing suitable fluorescence photoswitching property are introduced. Furthermore, the recent development of new applications using fluorescent diarylethene-based molecules and nanomaterials are also summarized.