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In a search for dyes photoactivatable with visible light, fluorenes with substituents at positions 2 and 7 were prepared, and their absorption and emission spectra were studied. In particular, the synthesis route to 9-diazofluorenes with 2-(N,N-dialkylamino) and N-modified 7-(4-pyridyl) substituents was established. These compounds are initially non-fluorescent, undergo photolysis with UV or blue light, and—in non-polar media—provide orange- to red-emitting products with a large separation between absorption and emission bands. Irradiation of non-fluorescent 9-diazoderivative 20 in dioxane with the light of 365 nm or 470 nm was accompanied by strong fluorescence gain (10 to 20 times), orange–red emission, and a large Stokes shift of photoproducts, which structurally relate to fluorescent betaine 13 (model compound without diazo group). Photolysis of 20 in protic solvents (ROH = MeOH, H2O) provided clean transformation to C9-OR derivatives, though the emission gain in protic solvents was low. [ABSTRACT FROM AUTHOR]

New photostable and bright supramolecular complexes based on cucurbit[7]uril (CB7) host and diketopyrrolopyrole (DPP) guest dyes having two positively charged 4‐(trimethylammonio)phenyl groups were prepared and characterized. The dye core displays large Stokes shift (in H2O, abs./emission max. 480/550 nm; ϵ~19 000, τfl>4 ns), strong binding with the host (~560 nM Kd) and a linker affording fluorescence detection of bioconjugates with antibody and nanobody. Combination of protein‐functionalized DPP dye with CB7 improves photostability and affords up to 12‐fold emission gain. Two‐color confocal and stimulated emission depletion (STED) microscopy with 595 nm or 655 nm STED depletion lasers shows that the presence of CB7 not only leads to improved brightness and image quality, but also results in DPP becoming cell‐permeable. [ABSTRACT FROM AUTHOR]

New photostable and bright supramolecular complexes based on cucurbit[7]uril (CB7) host and diketopyrrolopyrole (DPP) guest dyes having two positively charged 4‐(trimethylammonio)phenyl groups were prepared and characterized. The dye core displays large Stokes shift (in H2O, abs./emission max. 480/550 nm; ϵ~19 000, τfl>4 ns), strong binding with the host (~560 nM Kd) and a linker affording fluorescence detection of bioconjugates with antibody and nanobody. Combination of protein‐functionalized DPP dye with CB7 improves photostability and affords up to 12‐fold emission gain. Two‐color confocal and stimulated emission depletion (STED) microscopy with 595 nm or 655 nm STED depletion lasers shows that the presence of CB7 not only leads to improved brightness and image quality, but also results in DPP becoming cell‐permeable. [ABSTRACT FROM AUTHOR]

The single‐molecule localization concept MINFLUX has triggered a reevaluation of the features of fluorophores for attaining nanometer‐scale resolution. MINFLUX nanoscopy benefits from temporally controlled fluorescence ("on"/"off") photoswitching. Combined with an irreversible switching behavior, the localization process is expected to turn highly efficient and quantitative data analysis simple. The potential in the recently reported photoactivable xanthone (PaX) dyes is recognized to extend the list of molecular switches used for MINFLUX with 561 nm excitation beyond the fluorescent protein mMaple. The MINFLUX localization success rates of PaX560, PaX+560, and mMaple are quantitatively compared by analyzing the effective labeling efficiency of endogenously tagged nuclear pore complexes. The PaX dyes prove to be superior to mMaple and on par with the best reversible molecular switches routinely used in single‐molecule localization microscopy. Moreover, the rationally designed PaX595 is introduced for complementing PaX560 in dual color 561 nm MINFLUX imaging based on spectral classification and the deterministic, irreversible, and additive‐independent nature of PaX photoactivation is showcased in fast live‐cell MINFLUX imaging. The PaX dyes meet the demands of MINFLUX for a robust readout of each label position and fill the void of reliable fluorophores dedicated to 561 nm MINFLUX imaging. [ABSTRACT FROM AUTHOR]

We report on the synthesis of two fluorescent probes which can be activated by β-Galactosidase (β-Gal) enzymes and/or light. The probes contained 2-nitro-4-oxybenzyl and 3-nitro-4-oxybenzyl fragments, with β-Gal residues linked to C-4. We performed the enzymatic and photoactivation of the probes in a cuvette and compared them, prior to the labeling of Vimentin–Halo fusion protein in live cells with overexpressed β-galactosidase. The dye fluorescence afforded the observation of enzyme activity by means of confocal and super-resolution optical microscopy based on stimulated emission depletion (STED). The tracing of enzymatic activity with the retention of activated fluorescent products inside cells was combined with super-resolution imaging as a tool for use in biomedicine and life science. [ABSTRACT FROM AUTHOR]

New photoactivatable fluorescent dyes (rhodamine, carbo‐ and silicon‐rhodamines [SiR]) with emission ranging from green to far red have been prepared, and their photophysical properties studied. The photocleavable 2‐nitrobenzyloxycarbonyl unit with an alpha‐carboxyl group as a branching point and additional functionality was attached to a polycyclic and lipophilic fluorescent dye. The photoactivatable probes having the HaloTagTM amine (O2) ligand bound with a dye core were obtained and applied for live‐cell staining in stable cell lines incorporating Vimentin (VIM) or Nuclear Pore Complex Protein NUP96 fused with the HaloTag. The probes were applied in 2D (VIM, NUP96) and 3D (VIM) MINFLUX nanoscopy, as well as in superresolution fluorescence microscopy with single fluorophore activation (VIM, live‐cell labeling). Images of VIM and NUPs labeled with different dyes were acquired and their apparent dimensions and shapes assessed on a lower single‐digit nanometer scale. Applicability and performance of the photoactivatable dye derivatives were evaluated in terms of photoactivation rate, labeling and detection efficiency, number of detected photons per molecule and other parameters related to MINFLUX nanoscopy. [ABSTRACT FROM AUTHOR]

New photoactivatable fluorescent dyes (rhodamine, carbo‐ and silicon‐rhodamines [SiR]) with emission ranging from green to far red have been prepared, and their photophysical properties studied. The photocleavable 2‐nitrobenzyloxycarbonyl unit with an alpha‐carboxyl group as a branching point and additional functionality was attached to a polycyclic and lipophilic fluorescent dye. The photoactivatable probes having the HaloTagTM amine (O2) ligand bound with a dye core were obtained and applied for live‐cell staining in stable cell lines incorporating Vimentin (VIM) or Nuclear Pore Complex Protein NUP96 fused with the HaloTag. The probes were applied in 2D (VIM, NUP96) and 3D (VIM) MINFLUX nanoscopy, as well as in superresolution fluorescence microscopy with single fluorophore activation (VIM, live‐cell labeling). Images of VIM and NUPs labeled with different dyes were acquired and their apparent dimensions and shapes assessed on a lower single‐digit nanometer scale. Applicability and performance of the photoactivatable dye derivatives were evaluated in terms of photoactivation rate, labeling and detection efficiency, number of detected photons per molecule and other parameters related to MINFLUX nanoscopy. [ABSTRACT FROM AUTHOR]

Searching for photoconvertible or photoactivatable dyes, we considered trimethine (Cy3) and pentamethine (Cy5) fluorophores with a 4‐amino‐1‐diazo‐2‐butanone fragment (H2N(CH2)2COCH=N2) attached to the meso (γ) position of the polymethine chain via the amino group. The Cy3 derivative was prepared. All Cy5 derivatives with the basic amino group at this position decomposed with breaking the polymethine chain. However, amino‐squaraine based Cy5 dyes were found to be stable and accessible. Photolysis of Cy3 and squaraine‐based Cy5 dyes with a 4‐amino‐1‐diazo‐2‐butanone fragment was accompanied with Wolff rearrangement and led to pyrrolidones (in methanol and aprotic solvents) formed via intramolecular cyclization of the intermediate ketenes. In aqueous acetonitrile, ketenes reacted with water and gave carboxylic acids. Both products were non‐fluorescent, though the model Cy5 dyes (without the squaraine fragment) with acylated amino and N‐methylamino groups were found to be fluorescent. [ABSTRACT FROM AUTHOR]

The use of photoswitchable fluorescent diarylethenes (fDAEs) as protein labels in fluorescence microscopy and nanoscopy has been limited by labeling inhomogeneity and the need for ultraviolet light for fluorescence activation (on-switching). To overcome these drawbacks, we prepared "turn-on mode" fDAEs featuring thienyl substituents, multiple polar residues, and a reactive maleimide group in the core structure. Conjugates with antibodies and nanobodies displayed complete on-switching and excitation with violet (405 nm) and yellow-green (<565 nm) light, respectively. Besides, they afforded high signal-to-noise ratios and low unspecific labeling in fluorescence imaging. Irradiation with visible light at 532 nm or 561 nm led to transient on-off switching ("blinking") of the fDAEs of double-labeled nanobodies so that nanoscale superresolution images were readily attained through switching and localization of individual fluorophores. [ABSTRACT FROM AUTHOR]

Compact "push–pull" photochromic diaryethenes (DAEs) with unsymmetric oxidation pattern of the benzothiophene core display multicolour fluorescence switching, as a result of dual emission from both "open" and "closed" forms. These DAEs also present an unprecedented photo-fatigue resistance. [ABSTRACT FROM AUTHOR]

Electronic energy transfer (EET) between chromophores is of fundamental importance for many biological processes and optoelectronic devices. However, common models fall short in fully describing the process, especially in bichromophoric model systems with a donor and acceptor connected by a rigid linker providing perpendicular geometries. Herein, we report a novel strategy for preparing bichromophores containing adamantane or 2-(2-adamantylidene)adamantane as rigid spacers, providing a fixed distance between chromophores, and their parallel or perpendicular arrangement without chromophore rotation. New fluorophores were developed and linked via spiroatoms. Bichromophores with identical (blue-blue) or different (blue-red) chromophores were synthesized, either in orthogonal or parallel geometry. These were characterized by absorption/fluorescence spectroscopy, time-resolved fluorescence anisotropy, and fluorescence antibunching measurements. Based on the Förster point-dipole approximation, EET efficiencies were estimated by using geometrical parameters from (time-dependent) density functional calculations. For bichromophores with parallel geometry, the predicted EET efficiencies were near unity and fit the measurements. In spite of estimated values around 0.4 and 0.5, 100 % efficiency was observed also for bichromophores with orthogonal geometry. The new rigid scaffolds presented here open new possibilities for the synthesis of bichormophores with well-defined parallel or perpendicular geometry. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, structural analysis and fluorescence properties of two rhodamine 6G derivatives are described, namely a propargylamine derivative, 3',6'-bis(ethylamino)-2',7'-dimethyl-2-(methylcyanide)spiro[isoindole-1,9'-xanthen]-3(2H)-one (I), and a γ-aminobutyric acid (GABA) derivative, 3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindole-1,9'-xanthen]-2(3H)-yl)butyricacid (II). Both structures are compared with four similar ones from the Cambridge Structural Database (CSD), and the interactions involved in the stabilization are analyzed using the atoms in molecules (AIM) theory. Finally, a single-crystal in-situ reaction study is presented, carried out by fluorescence methods, which enabled the 'opening' of the spirolactam ring in the solid phase. [ABSTRACT FROM AUTHOR]

Large Stokes-shift coumarin dyes with an O-phosphorylated 4-(hydroxymethyl)-2,2-dimethyl-1,2,3,4-tetrahydroquinoline fragment emitting in the blue, green, and red regions of the visible spectrum were synthesized. For this purpose, N-substituted and O-protected 1,2-dihydro-7-hydroxy-2,2,4-trimethylquinoline was oxidized with SeO2 to the corresponding α,β-unsaturated aldehyde and then reduced with NaBH4 in a 'one-pot' fashion to yield N-substituted and 7- O-protected 4-(hydroxymethyl)-7-hydroxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoline as a common precursor to all the coumarin dyes reported here. The photophysical properties of the new dyes ('reduced coumarins') and 1,2-dihydroquinoline analogues (formal precursors) with a trisubstituted C=C bond were compared. The 'reduced coumarins' were found to be more photoresistant and brighter than their 1,2-dihydroquinoline counterparts. Free carboxylate analogues, as well as their antibody conjugates (obtained from N-hydroxysuccinimidyl esters) were also prepared. All studied conjugates with secondary antibodies afforded high specificity and were suitable for fluorescence microscopy. The red-emitting coumarin dye bearing a betaine fragment at the C-3-position showed excellent performance in stimulation emission depletion (STED) microscopy. [ABSTRACT FROM AUTHOR]

Caged rhodamine dyes (Rhodamines NN) of five basic colors were synthesized and used as 'hidden' markers in subdiffractional and conventional light microscopy. These masked fluorophores with a 2-diazo-1-indanone group can be irreversibly photoactivated, either by irradiation with UV- or violet light (one-photon process), or by exposure to intense red light ( λ∼750 nm; two-photon mode). All dyes possess a very small 2-diazoketone caging group incorporated into the 2-diazo-1-indanone residue with a quaternary carbon atom (C-3) and a spiro-9 H-xanthene fragment. Initially they are non-colored (pale yellow), non-fluorescent, and absorb at λ=330-350 nm (molar extinction coefficient (ε)≈104 M−1 cm−1) with a band edge that extends to about λ=440 nm. The absorption and emission bands of the uncaged derivatives are tunable over a wide range ( λ=511-633 and 525-653 nm, respectively). The unmasked dyes are highly colored and fluorescent ( ε= 3-8×104 M−1 cm−1 and fluorescence quantum yields ( ϕ)=40-85 % in the unbound state and in methanol). By stepwise and orthogonal protection of carboxylic and sulfonic acid groups a highly water-soluble caged red-emitting dye with two sulfonic acid residues was prepared. Rhodamines NN were decorated with amino-reactive N-hydroxysuccinimidyl ester groups, applied in aqueous buffers, easily conjugated with proteins, and readily photoactivated (uncaged) with λ=375-420 nm light or intense red light ( λ=775 nm). Protein conjugates with optimal degrees of labeling (3-6) were prepared and uncaged with λ=405 nm light in aqueous buffer solutions ( ϕ=20-38 %). The photochemical cleavage of the masking group generates only molecular nitrogen. Some 10-40 % of the non-fluorescent (dark) byproducts are also formed. However, they have low absorbance and do not quench the fluorescence of the uncaged dyes. Photoactivation of the individual molecules of Rhodamines NN (e.g., due to reversible or irreversible transition to a 'dark' non-emitting state or photobleaching) provides multicolor images with subdiffractional optical resolution. The applicability of these novel caged fluorophores in super-resolution optical microscopy is exemplified. [ABSTRACT FROM AUTHOR]

The spatial resolution of fluorescence microscopes is limited by diffraction to about half of the light wavelength, hampering the observation of many important intracellular processes. Recent emerging techniques have overcome that diffraction barrier using the temporal discrimination of close objects that are otherwise unresolved or blurred within the spatial resolution of the microscope. The key of these techniques is to switch the signal of fluorescence markers on and off exploiting their distinct molecular states, and detect and localize these markers at the single-molecule level. This underlying principle highlights the critical role of the photophysical properties of the probes, and the importance of finding adequate switching mechanisms. Here, we present strategies to achieve fluorescence modulation based on novel molecular assemblies containing a [1,3]oxazine as the two states, building block responsible for the transformation. Two different triggering events, based on the photochromic and halochromic properties of the oxazine, induce a large absorption and emission bathochromic shift of a pendant fluorophore, as the ultimate fluorescence switching event. The implementation of these approaches to achieve spatial resolution beyond the diffraction limit is also discussed. [ABSTRACT FROM AUTHOR]

Spatial resolution in far-field fluorescence microscopy is limited by diffraction to about 200 nm. With the aid of photoswitchable fluorophores, the diffraction barrier has been successfully overcome, allowing unprecedented resolution in the order of single biomolecules. The imaging process demands markers with strict and reliable control of the switching, to keep most of the markers in a non-emissive state most of the time and to bring a tiny number back to an emissive state, and detection at the single-molecule level. Herein, we describe the use of rhodamine spiroamides with unique photophysical properties as molecular probes for super-resolution techniques based on the localization of single emitters. This family of photochromic and fluorescent compounds fulfils the stringent requirements for such imaging methods; these compounds are robust and capable of enduring single-molecule detection in diverse environments. This has allowed meaningful images with resolution down to a few nanometres. Their design, synthesis and implementation is discussed along with imaging applications in material and life sciences. [ABSTRACT FROM AUTHOR]

We investigate the equilibrium, kinetics, and mechanism of the photochromic transformation of a series of amido spirorhodamine compounds―differing in the nature of the substituents of the amido group and in the rhodamine chromophore―in ethanol at room temperature in the presence of trifluoroacetic acid. A proton participates in the equilibrium between the spiro form and the open rhodamine form. The relaxation times in the dark or under continuous irradiation show a linear dependence on the proton concentration. The slopes of these plots show a linear free energy relation with the equilibrium constant of the transformation. A mechanism involving reversible reaction steps between four states: the two thermodynamically stable isomers, a protonated spiro form, and a deprotonated open form, can account for the kinetic observations in the dark and under irradiation. [ABSTRACT FROM AUTHOR]

Caged near-IR emitting fluorescent dyes are in high demand in optical microscopy but up to now were unavailable. We discovered that the combination of a carbopyronine dye core and a photosensitive 2-diazo-1-indanone residue leads to masked near-IR emitting fluorescent dyes. Illumination of these caged dyes with either UV or visible light (λ ＜ 420 nm) efficiently generates fluorescent compounds with absorption and emission at 635 nm and 660 nm, respectively. A high-yielding synthetic route with attractive possibilities for further dye design is described in detail. Good photostability, high contrast, and a large fluorescence quantum yield after uncaging are the most important features of the new compounds for non-invasive imaging in high-resolution optical microscopy. For use in immunolabelling the caged dyes were decorated with a (hydrophilic) linker and an (activated) carboxyl group. [ABSTRACT FROM AUTHOR]

Reversibly photoswitchable diarylethenes (DAEs) with fluorescent closed forms are applied in biology‐ and material science‐related super‐resolution microscopy. Yet, their full photoswitchable capacities remain unrevealed and unexplored. Due to limitations in synthesis, only 1,2‐[bis‐(2‐ethyl‐1‐benzothiophene‐1,1‐dioxide‐3‐yl)]perfluorocyclopentenes with two identical or very similar aryl groups attached to C‐6 and C‐6′ have been prepared so far. DAEs with increased Stokes shifts related to asymmetric structures and the presence of "push–pull" substituents are introduced in the present study, and their switching power is studied. The new "simplified" asymmetric DAEs possess higher cycloreversion quantum yields, but lower emission efficiencies than their known analogs with extended π‐conjugation paths. Fatigue resistance in organic (acetonitrile and methanol) and aqueous solvents is studied, and the performance in reversible saturable optical fluorescence transition (RESOLFT) microscopy is evaluated. The push–pull structures show an outstanding increase in fatigue resistance, compared with a reference (H/H) diarylethene. Fatigue resistances on the order of thousands of cycles have been observed in acetonitrile solutions without exclusion of air oxygen. The structure–property relationships and facile preparation procedures enable rational design of DAEs applicable as photoswitchable fluorescent probes. A new setup and methodology for measuring switching performance of fluorescent DAEs are introduced. Design and synthesis of diarylethenes (DAEs) with oxidized 2‐alkylbenzothiophen‐3‐yl units provide asymmetric compact switchers undergoing reversible transitions between light‐emitting and "dark" states. The reported preparation, spectral properties, switching kinetics, fatigue‐resistance, bioconjugation, and super‐resolution microscopy applications enable rational design of DAEs with better switching performance. [ABSTRACT FROM AUTHOR]

Die Polarität und Beweglichkeit …… mehrerer Carboxyreste verleihen einem photochromen Fluorophor die Fähigkeit zu reversiblem Schalten in rein wässrigen Lösungen, wie V. N. Belov, M. Irie, S. W. Hell et al. in der Zuschrift auf S. 15655 ff. beschreiben. Die synthetische symmetrische “Octacarbonsäure” kopiert die natürliche Bewegung von Fischflossen ebenso wie ihre anmutige Funktion in Wasser. Bildlayout: H. Sebesse. [ABSTRACT FROM AUTHOR]

The cover page of the journal "Angewandte Chemie International Edition" is presented.

Invited for the cover of this issue are Prof. Stefan W. Hell, Dr. Vladimir N. Belov, and co-workers at Max Planck Institute for Biophysical Chemistry (Göttingen, Germany), University of Buenos-Aires (Argentina), and Chemistry Department of St. Petersburg State University (Russia). The image (including artwork by Vladimir Belov and Hartmut Sebesse, MPIbpc, Göttingen) depicts the light-induced transformations that occur in nature and in Rhodamines NN masked fluorescent dyes. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

All the beauty is revealed when sunlight shines on the statue of Polymnia, one of the nine Muses in ancient Greek mythology, masked with snow in winter and then liberated in all its splendor from the white cloak by bright sunshine. The parallel light ‐ induced transformation is depicted by the chemical formulae. Irradiation of colorless Rhodamines NN, masked fluorescent dyes, with UV or visible light irreversibly “releases” the hidden colors in all their depth and vibrant fluorescence. For more details, see the Full Paper by V. N. Belov, M. L. Bossi, S. W. Hell et al. on page 13162 ff. [ABSTRACT FROM AUTHOR]