Abstract
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.
Highlights
Molecules that can reversibly change in response to external stimuli are of central importance to the development of molecular devices and memory materials and to pharmacology and imaging technologies[1–5]
Upon irradiation with 680 nm light to the dark state solution, the fluorescence intensity of 9 gradually increased and perfectly recovered up to the initial level, while the fluorescence intensity of 17 never changed, even after irradiation for an extended period, because 17 has no absorption at this wavelength. These results clearly indicated that the fluorescence photoswitching of 9 and 17 can be selectively modulated by optimizing the irradiation wavelength condition appropriately
In most of the systems, RET is responsible for the fluorescence photoswitching: the fluorophore is fully emissive when the DAE is in its open form, whereas it is a FF
Summary
Wöll et al.[82] demonstrated PALM super-resolution imaging of block copolymer cylindrical micelles forming string structures by using a turn-on-type DAE derivative for which the closed-ring isomer of DAEbearing sulfone groups is fluorescent In this example, the resolution was estimated to be approximately 50 nm with respect to full-width at half-maximum (FWHM). These derivatives are soluble in phosphatebuffered saline (PBS) buffer solution and exhibit reversible fluorescence photoswitching with relatively high contrast and fluorescence quantum yield (>0.3) They first performed RESOLFT super-resolution imaging of fixed immune-labeled Vero cells by using the symmetrical DAE derivative 12 having eight carboxylic acid groups and achieved ~74-nm spatial resolution with respect to the FWHM (Fig. 13b)[83]. Upon sequential irradiation with 313 nm light, the cyan-emission band completely disappeared and a O DAE O
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