A combined experimental–theoretical investigation has revealed that oxazine-based compounds are multiaddressable, multistate, and multifunctional molecular switches exhibiting contrasts of both ...linear and second-order nonlinear optical properties. The switching properties are particularly large when the substituent is a donor group. In this study, the cleavage of the C–O bond at the junction of the indole and oxazine cycles (of the closed a forms) is acido-triggered, leading to an open form (b + ) characterized by larger first hyperpolarizabilities (βHRS) and smaller excitation energies than in the closed form. These results are confirmed and interpreted utilizing ab initio calculations that have been carried out on a broad set of compounds to unravel the role of the substituent. With respect to acceptor groups, oxazines bearing donor groups are characterized not only by larger βHRS and βHRS contrast ratios but also by smaller excitation energies, larger opening-induced charge transfer, and reduction of the bond length alternation, as well as smaller Gibbs energies of the opening reaction. Compared to protonated open forms (b + ), calculations on the zwitterionic open forms (b) have pointed out similarities in the long-wavelength UV/vis absorption spectra, whereas their βHRS values might differ strongly as a function of the substituent. Indeed, the open forms present two NLOphores, the indoleninium-substituent entity and the nitrophenol (present in the protonated open form, b + ) or nitrophenolate (present in the zwitterionic open form, b) moiety. Then, nitrophenolate displays a larger first hyperpolarizability than nitrophenol and the β tensor of the two entities might reinforce or cancel each other.
Optical diffraction fundamentally limits the spatial resolution of conventional fluorescence images to length scales that are, at least, 2 orders of magnitude longer than the dimensions of individual ...molecules. As a result, the development of innovative probes and imaging schemes to overcome diffraction is very much needed to enable the investigation of the fundamental factors regulating cellular functions at the molecular level. In this context, the chemical synthesis of molecular constructs with photoactivatable fluorescence and the ability to label subcellular components of live cells can have transformative implications. Indeed, the fluorescence of the resulting assemblies can be activated with spatiotemporal control, even in the intracellular environment, to permit the sequential localization of individual emissive labels with precision at the nanometer level and the gradual reconstruction of images with subdiffraction resolution. The implementation of these operating principles for subdiffraction imaging, however, is only possible if demanding photochemical and photophysical requirements to enable photoactivation and localization as well as stringent structural requisites to allow the covalent labeling of intracellular targets in live cells are satisfied. Because of these complications, only a few synthetic photoactivatable fluorophores with appropriate performance for live-cell imaging at the nanoscale have been developed so far. Significant synthetic efforts in conjunction with spectroscopic analyses are still very much needed to advance this promising research area further and turn photoactivatable fluorophores into the imaging probes of choice for the investigation of live cells.
The photoinduced disconnection of an oxazine heterocycle from a borondipyrromethene (BODIPY) chromophore activates bright far-red fluorescence. The high brightness of the product and the lack of ...autofluorescence in this spectral region allow its detection at the single-molecule level within the organelles of live cells. Indeed, these photoactivatable fluorophores localize in lysosomal compartments and remain covalently immobilized within these organelles. The suppression of diffusion allows the reiterative reconstruction of subdiffraction images and the visualization of the labeled organelles with excellent localization precision. Thus, the combination of photochemical, photophysical and structural properties designed into our fluorophores enable the visualization of live cells with a spatial resolution that is inaccessible to conventional fluorescence imaging.
On-command changes in the emission color of functional materials is a sought-after property in many contexts. Of particular interest are systems using light as the external trigger to induce the ...color changes. Here we report on a tri-component cocktail consisting of a fluorescent donor molecule and two photochromic acceptor molecules encapsulated in polymer micelles and we show that the color of the emitted fluorescence can be continuously changed from blue-to-green and from blue-to-red upon selective light-induced isomerization of the photochromic acceptors to the fluorescent forms. Interestingly, isomerization of both acceptors to different degrees allows for the generation of all emission colors within the red-green-blue (RGB) color system. The function relies on orthogonally controlled FRET reactions between the blue emitting donor and the green and red emitting acceptors, respectively.
Photochemical Barcodes Tang, Sicheng; Zhang, Yang; Dhakal, Pravat ...
Journal of the American Chemical Society,
04/2018, Letnik:
140, Številka:
13
Journal Article
Recenzirano
Odprti dostop
A photochemical strategy to encode fluorescence signals in vivo with spatial control was designed around the unique properties of a photoactivatable borondipyrromethene (BODIPY). The photoinduced ...disconnection of two oxazines, flanking a single BODIPY, in two consecutive steps produces a mixture of three emissive molecules with resolved fluorescence inside polymer beads. The relative amounts and emission intensities of the three fluorophores can be regulated precisely in each bead by adjusting the dose of activating photons to mark individual particles with distinct codes of fluorescence signals. The visible wavelengths and mild illumination sufficient to induce these transformations permit the photochemical barcoding of beads also in living nematodes. Different regions of the same animal can be labeled with distinct barcodes to allow the monitoring of their dynamics for long times with no toxic effects. Thus, our photochemical strategy for the generation of fluorescence barcodes can produce multiple and distinguishable labels in the same biological sample to enable the spatiotemporal tracking of, otherwise indistinguishable, targets.
The borondipyrromethene (BODIPY) chromophore is a versatile platform for the construction of photoresponsive dyes with unique properties. Specifically, its covalent connection to a photocleavable ...group can be exploited to engineer compounds with photoswitchable fluorescence. The resulting photoactivatable fluorophores can increase their emission intensity or shift their emission wavelengths in response to switching. Such changes permit the spatiotemporal control of fluorescence with optical stimulations and the implementation of imaging strategies that would be impossible to replicate with conventional fluorophores. Indeed, BODIPYs with photoactivatable fluorescence enable the selective highlighting of intracellular targets, the nanoscaled visualization of sub‐cellular components, the real‐time monitoring of dynamic events and the photochemical writing of optical barcodes.
Photoactivatable BODIPYs permit fluorescence switching with spatiotemporal control under the influence of optical stimulations. Their synthetic versatility further provides the opportunity to engineer the photochemical, photophysical and structural properties for the implementation of invaluable imaging strategies aimed at elucidating the structures and dynamics of biological samples. Specifically, these photoactivatable fluorophores allow the visualization of live cells with sub‐diffraction resolution and the monitoring of dynamic events in live organisms.
We synthesized five fluorophore–photochrome dyads designed to switch reversibly between nonfluorescent and fluorescent isomers under optical control. These compounds pair an oxazine photochrome to a ...biphenyl, fluorene, pyrene, coumarin, or cyanine fluorophore in their molecular skeleton and can be prepared in a single step from known precursors in yields ranging from 30 to 63%. Nuclear magnetic resonance spectroscopy indicates that the oxazine ring of these compounds opens and closes spontaneously on a millisecond time scale in acetonitrile at ambient temperature. Under these conditions, the fraction of ring-open isomer at equilibrium is negligible in all instances with the exception of the cyanine derivative, which instead is almost exclusively in this form. Absorption and emission spectroscopies demonstrate, however, that the fraction of ring-open isomer is sensitive to solvent polarity and increases with a transition from acetonitrile to methanol. Alternatively, the ring-open isomer can be populated photochemically or trapped with the addition of acid. In both instances, the characteristic absorption and emission bands of the 3H-indolium chromophores, embedded within the ring-open species, can clearly be observed in the visible region. In the case of the coumarin derivative, the brightness of this chromophoric fragment is sufficiently high to permit the imaging of individual molecules with excellent signal-to-noise ratios. In fact, the fluorescence of single fluorophore–photochrome dyads can be activated under the influence of ultraviolet inputs and the resulting species can be localized with nanoscale precision under visible illumination. Indeed, subdiffraction images of polymer nanoparticles, doped with this particular dyad, can be reconstructed with nanoscale resolution. Thus, our operating principles for fluorescence switching at the single-molecule level can offer the opportunity to overcome diffraction and, eventually, lead to the development of an entire family of probes for super-resolution fluorescence imaging.
A water-soluble thermochromic molecular switch with spectrally resolved fluorescence in its two interconvertible states can be assembled in three synthetic steps by integrating a fluorescent coumarin ...chromophore, a hydrophilic oligo(ethylene glycol) chain, and a switchable oxazole heterocycle in the same covalent skeleton. Measurements of its two emissions in separate detection channels of a fluorescence microscope permit the noninvasive and ratiometric sensing of temperature at the micrometer level with millisecond response in aqueous solutions and within hydrogel matrices. The ratiometric optical output of this fluorescent molecular switch overcomes the limitations of single-wavelength fluorescent probes and enables noninvasive temperature mapping at length scales that are not accessible to conventional thermometers based on physical contact.
Self-assembling nanoparticles of amphiphilic polymers can transport hydrophobic molecules across hydrophilic media and, as a result, can be valuable delivery vehicles for a diversity of biomedical ...applications. Strategies to monitor their dynamics noninvasively and in real time are, therefore, essential to investigate their translocation within soft matrices and, possibly, rationalize the mechanisms responsible for their diffusion in biological media. In this context, we designed molecular guests with photoactivatable fluorescence for these supramolecular hosts and demonstrated that the activation of the fluorescent cargo, under optical control, permits the tracking of the nanocarrier translocation across hydrogel matrices with the sequential acquisition of fluorescence images. In addition, the mild illumination conditions sufficient to implement these operating principles permit fluorescence activation within developing Drosophila melanogaster embryos and enable the monitoring of the loaded nanocarriers for long periods of time with no cytotoxic effects and no noticeable influence on embryogenesis. These photoresponsive compounds combine a borondipyrromethene (BODIPY) chromophore and a photocleavable oxazine within their covalent skeleton. Under illumination at an appropriate activation wavelength, the oxazine ring cleaves irreversibly to bring the adjacent BODIPY fragment in conjugation with an indole heterocycle. This structural transformation shifts bathochromically the BODIPY absorption and permits the selective excitation of the photochemical product with concomitant fluorescence. In fact, these operating principles allow the photoactivation of BODIPY fluorescence with large brightness and infinite contrast. Thus, our innovative structural design translates into activatable fluorophores with excellent photochemical and photophysical properties as well as provides access to a general mechanism for the real-time tracking of supramolecular nanocarriers in hydrophilic matrices.
The stringent limitations imposed by diffraction on the spatial resolution of fluorescence microscopes demand the identification of viable strategies to switch fluorescence under optical control. In ...this context, the photoinduced and reversible transformations of photochromic compounds are particularly valuable. In fact, these molecules can be engineered to regulate the emission intensities of complementary fluorophores in response to optical stimulations. On the basis of this general design logic, we assembled a functional molecular construct consisting of a borondipyrromethene fluorophore and a nitrospiropyran photochrome and demonstrated that the emission of the former can be modulated with the interconversion of the latter. This fluorophore–photochrome dyad, however, has a slow switching speed and poor fatigue resistance. To improve both parameters, we developed a new family of photochromic switches based on the photoinduced opening and thermal closing of an oxazine ring. These compounds switch back and forth between ring-closed and -open isomers on nanosecond–microsecond timescales and tolerate thousands of switching cycles with no sign of degradation. In addition, the attachment of appropriate chromophoric fragments to their switchable oxazine ring can be exploited to either deactivate or activate fluorescence reversibly in response to illumination with a pair of exciting beams. Specifically, we assembled three dyads, each based on either a borondipyrromethene or a coumarin fluorophore and an oxazine photochrome, and modulated their fluorescence in a few microseconds with outstanding fatigue resistance. The unique photochemical and photophysical properties of our fluorophore–photochrome dyads can facilitate the development of switchable fluorophores for superresolution imaging and, ultimately, provide valuable molecular probes for the visualization of biological samples on the nanometer level.
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