Reversible rot fluoreszierende molekulare Schalter

Photochemical Mechanisms of Fluorophores Employed in Single-Molecule Localization Microscopy

Decoding cellular processes requires visualization of the spatial distribution and dynamic interactions of biomolecules. It is therefore not surprising that innovations in imaging technologies have facilitated advances in biomedical research. The advent of super-resolution imaging technologies has empowered biomedical researchers with the ability to answer long-standing questions about cellular processes at an entirely new level. Fluorescent probes greatly enhance the specificity and resolution of super-resolution imaging experiments. Here, we introduce key super-resolution imaging technologies, with a brief discussion on single-molecule localization microscopy (SMLM). We evaluate the chemistry and photochemical mechanisms of fluorescent probes employed in SMLM. This Review provides guidance on the identification and adoption of fluorescent probes in single molecule localization microscopy to inspire the design of next-generation fluorescent probes amenable to single-molecule imaging.

Carboxylated Photoswitchable Diarylethenes for Biolabeling and Super-Resolution RESOLFT Microscopy

Reversibly photoswitchable 1,2‐bis(2‐ethyl‐6‐phenyl‐1‐benzothiophene‐1,1‐dioxide‐3‐yl)perfluorocyclopentenes (EBT) having fluorescent “closed” forms were decorated with four or eight carboxylic groups and attached to antibodies. Low aggregation, efficient photoswitching in aqueous buffers, specific staining of cellular structures, and good photophysical properties were demonstrated. Alternating light pulses of UV and blue light induce numerous reversible photochemical transformations between two stables states with distinct structures. Using relatively low light intensities, EBTs were applied in biology‐related super‐resolution microscopy based on the reversible saturable (switchable) optical linear fluorescence transitions (RESOLFT) and demonstrated optical resolution of 75 nm.

Reversible Photomodulation of Electronic Communication in a π-Conjugated Photoswitch-Fluorophore Molecular Dyad

The extent of electronic coupling between a boron dipyrromethene (BODIPY) fluorophore and a diarylethene (DAE) photoswitch has been modulated in a covalently linked molecular dyad by irradiation with either UV or visible light. In the open isomer, both moieties can be regarded as individual chromophores, while in the closed form the lowest electronic (S0 →S1 ) transition of the dyad is slightly shifted, enabling photomodulation of its fluorescence. Transient spectroscopy confirms that the dyad behaves dramatically different in the two switching states: while in the open isomer it resembles an undisturbed BODIPY fluorophore, in the closed isomer no fluorescence occurs and instead a red-shifted DAE behavior prevails.

Photo-driven near-IR fluorescence switch: synthesis and spectroscopic investigation of squarine-spiropyran dyad

Novel NIR fluorescent dyad was synthesized using Squarine derivatives (SQ) and Spiropyran (SP) and characterized. Light driven reversible changes between two isomers of SP modulate the fluorescence of SQ leading to ON/OFF switching behaviors.

Rhodamine F: a novel class of fluorous ponytailed dyes for bioconjugation

Incorporation of fluorous ponytails such as polyfluorinated alkyl residues (CH2)m(CF2)nCF3 leads to a novel class of bright rhodamine-based fluorescence dyes. These dyes combine the excellent photophysical properties of the frequently used rhodamine dyes with the unique features of "light" fluorous molecules. One of those features is the possibility to separate substances utilizing fluorous solid-phase extraction (F-SPE), which is based on the specific intermolecular interaction between fluorous compounds. Thus, molecules, which are labeled with these new dyes, are not only accessible to fluorescence experiments, but can also be easily purified (via so-called FluoroFlash columns) prior to use. The dyes were bound to a cell penetrating peptoid (polycationic oligo(N-substituted) glycine) on solid supports. These conjugates were purified with F-SPE before their photophysical and biological properties were investigated.

A photoswitchable poly(3-hexylthiophene)

A well-defined main-chain conjugated photoswitchable poly(3-hexylthiophene) with homogeneous hydrogen end groups was synthesized. Opening and closing the photoswitch enables reversible modulation of P3HT emission, which is quenched by 70% when the switch is closed. The optical properties during switching cycles were quantified by irradiation/spectroscopy sequences.

Photostable, amino reactive and water-soluble fluorescent labels based on sulfonated rhodamine with a rigidized xanthene fragment

Highly water soluble fluorescent dyes were synthesized and transformed into new amino reactive fluorescent labels for biological microscopy. To this end, rhodamine 8 (prepared from 7-hydroxy-1,2,3,4-tetrahydroquinoline (7) and phthalic anhydride in 85 % aq. H(3)PO(4)) was sulfonated with 30 % SO(3) in H(2)SO(4) and afforded the water soluble disulfonic acid 3 a (64 %). Amidation of the carboxy group in 3 a with 2-(methylamino)ethanol in the presence of O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluroniumPF(6) (-) (HATU) led to alcohol 3 b (66 %), which was transformed into the amino reactive mixed carbonate 3 d with di(N-succinimidyl)carbonate and Et(3)N. Reaction of the carboxy group in 3 a with MeNH(CH(2))(2)CO(2)Me and N,N,N',N'-tetramethyl-O-(N-succinimidyl)-uroniumBF(4) (-) (TSTU) yielded methyl ester 13. After saponification of the aliphatic carboxy group in 13, the compound was converted into NHS-ester 3 e (using HATU and Et(3)N). Heating of 7 with trimellitic anhydride in H(3)PO(4) gave a mixture of dicarboxylic acids 14 and 15 (1:1). Regioisomer 15 was isolated, sulfonated with 30 % SO(3) in H(2)SO(4), and disulfonic acid 3 f was used for the synthesis of the mono NHS-ester 3 g, in which the sterically unhindered carboxy group was selectively activated (with N-hydroxysuccinimide, HATU, and Et(3)N). The sulfonated rhodamines 3 b, c and f are soluble in water (up to 0.1 M), have excellent photostabilities and large fluorescence quantum yields. Subdiffraction resolution images of tubulin filaments of mammalian cells stained with these dyes illustrate their applicability as labels for stimulated emission depletion microscopy and other fluorescence techniques.

Synthesis and characterization of photoswitchable fluorescent silica nanoparticles

We have designed and synthesized a new functional (amino reactive) highly efficient fluorescent molecular switch (FMS) with a photochromic diarylethene and a rhodamine fluorescent dye. The reactive group in this FMS -N-hydroxysuccinimide ester- allows selective labeling of amino containing molecules or other materials. In ethanolic solutions, the compound displays a large fluorescent quantum yield of 52 % and a large fluorescence modulation ratio (94 %) between two states that may be interconverted with red and near-UV light. Silica nanoparticles incorporating the new FMS were prepared and characterized, and their spectroscopic and switching properties were also studied. The dye retained its properties after the incorporation into the silica, thereby allowing light-induced reversible high modulation of the fluorescence signal of a single particle for up to 60 cycles, before undergoing irreversible photobleaching. Some applications of these particles in fluorescence microscopy are also demonstrated. In particular, subdiffraction images of nanoparticles were obtained, in the focal plane of a confocal microscope.