Nanoscopic Visualization of Soft Matter Using Fluorescent Diarylethene Photoswitches

Abstract

The in situ imaging of soft matter is of paramount importance for a detailed understanding of functionality on the nanoscopic scale. Although super-resolution fluorescence microscopy methods with their unprecedented imaging capabilities have revolutionized research in the life sciences, this potential has been far less exploited in materials science. One of the main obstacles for a more universal application of superresolved fluorescence microscopy methods is the limitation of readily available suitable dyes to overcome the diffraction limit. Here, we report a novel diarylethene-based photoswitch with a highly fluorescent closed and a nonfluorescent open form. Its photophysical properties, switching behavior, and high photostability make the dye an ideal candidate for photoactivation localization microscopy (PALM). It is capable of resolving apolar structures with an accuracy far beyond the diffraction limit of optical light in cylindrical micelles formed by amphiphilic block copolymers.The nanoscopic structure of soft-matter materials determines their properties. [1] Therefore, methods to directly visualize structures in the nanometer range are of paramount importance for the ongoing evolution of novel materials with specialized and adaptive properties for sophisticated applications. Scanning probe microscopy techniques give access to the nanometer range and determine surface properties such as topology and softness, [2,3] while modern electron microscopy methods, such as scanning electron microscopy (SEM) [4,5] and transmission electron microscopy (TEM), [6][7][8] can yield structural information even in the subnanometer range when there is sufficient electron density contrast. Despite the success of these methods, they are technically demanding and time-consuming. Furthermore, many softmatter samples possess poor electron contrast, and require non-invasive in situ imaging below the surface as well as the possibility to directly study dynamics. In recent years, superresolved fluorescence microscopy has revolutionized optical imaging, [9][10][11][12][13][14] by utilizing the photophysical or photochemical switching of fluorescent dyes in a sophisticated manner in combination with modern optics. So far, the life sciences have benefited, in particular, from the new possibilities of resolving structures well beyond the diffraction limit of light. Only a few examples of the application of super-resolution microscopy to materials science have been reported, [15][16][17][18] since concepts that require, for example, the addition of (polar) switching buffers often fail for these systems. Therefore, the main bottleneck for more universal applications of super-resolution imaging are switchable dyes with suitable (photo-)physical and chemical properties, such as high photostability, adjustable switching rates, minimum interaction with the environment to be probed, and simple design, with the possibility of multiple and straightforward derivatization for the specific labeling of structures or compartments. [19] ...

Photoswitchable Turn-on Mode Fluorescent Diarylethenes: Strategies for Controlling the Switching Response

“…It is capable of resolving apolar nanostructures in cylindrical micelles formed by amphiphilic block copolymers by using super-resolution PALM. 74 The progress of super-resolution microscopy technique is continuing. Recently, Hell and co-workers 78 reported a new nanometer-resolution imaging method named MINFLUX.…”

Fluorescent Diarylethene Photoswitches—A Universal Tool for Super‐Resolution Microscopy in Nanostructured Materials

“…The visualization, with the above described methods, of apolar structures found in material science is often impossible since the employed polar switching buffers cannot significantly access apolar structures, whereas fluorescent proteins, if appropriate to be used, would denature under such conditions. As a consequence, super‐resolution microscopy has so far not been used extensively to address topics in soft matter or polymer science …”

“…Despite the multitude of different diarylethene derivatives available, only few of them exhibit, in their closed form, strong fluorescence in the visible range in conjunction with adjustable switching rates. As a consequence, their application for SRI has been limited so far …”

Turn‐On Fluorescent Photochromic Disulfonylarylthiophenes: Effect of Sulfone Groups on Fluorescence and Conversion

“…[3][4][5][6][7] The most common strategy for fluorescence switching is the coupling of a photochromic material with a fluorophore. [3][4][5][6][7] The most common strategy for fluorescence switching is the coupling of a photochromic material with a fluorophore.…”