Emission color tuning and white-light generation based on photochromic control of energy transfer reactions in polymer micelles

We encapsulate a fluorescent donor molecule and a photochromic acceptor unit (photoswitch) in polymer micelles and show that the color of the emitted fluorescence is continuously changed from blue to yellow upon light-induced isomerization of the acceptor. Interestingly, white-light generation is achieved in between. With the photoswitch in the colorless form, intense blue emission from the donor is observed, while UV-induced isomerization to the colored form induces an energy transfer reaction that quenches the donor emission and sensitizes the yellow emission from the colored photoswitch. The process is reversed by exposure to visible light, triggering isomerization to the colorless form

An all-photonic full color RGB system based on molecular photoswitches

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

Computational insights on the isomerization of photochromic oxazines

We investigated the isomerization of the simplest member of a family of photochromic oxazines with the aid of density functional theory, using three different functionals. Specifically, we simulated the thermal interconversion of the two enantiomers, associated with this compound, and established that the opening of the oxazine ring dictates the rate of the overall degenerate process. The M062X functional provides the best match to experimental data, whereas B3LYP calculations fail to model accurately the ground-state potential-energy surface of this system. In addition, we also modeled the absorption spectra of this compound and its photogenerated isomer with time-dependent calculations. The resulting data support the original assignment of the experimental spectra and confirm that the oxazine ring opens upon excitation. The MPW1PW91 functional provides the best match to experimental data, whereas M062X calculations fail to model accurately the spectroscopic parameters of this particular system. Furthermore, the MPW1PW91 calculations demonstrate that the photoinduced opening of the oxazine ring occurs along the potential-energy surface of the first triplet excited state. Indeed, the photoinduced isomerization appears to involve: (1) the initial excitation of one isomer to the second singlet excited state, (2) its thermal relaxation to the first triplet excited state, (3) its ring opening to produce the other isomer, and (4) the thermal relaxation of the product to the ground state. Thus, our calculations provide valuable information on the elementary steps governing the isomerization of this particular photochromic compound in the ground state and upon excitation. These useful mechanistic insights can guide the design of novel members of this family of photoresponsive compounds with specific properties

Photoactivatable Fluorophores

Photoactivatable fluorophores switch from a nonemissive to an emissive state upon illumination at an activating wavelength and then emit after irradiation at an exciting wavelength. The interplay of such activation and excitation events can be exploited to switch fluorescence on in a defined region of space at a given interval of time. In turn, the spatiotemporal control of fluorescence translates into the opportunity to implement imaging and spectroscopic schemes that are not possible with conventional fluorophores. Specifically, photoactivatable fluorophores permit the monitoring of dynamic processes in real time as well as the reconstruction of images with subdiffraction resolution. These promising applications can have a significant impact on the characterization of the structures and functions of biomolecular systems. As a result, strategies to implement mechanisms for fluorescence photoactivation with synthetic fluorophores are particularly valuable. In fact, a number of versatile operating principles have already been identified to activate the fluorescence of numerous members of the main families of synthetic dyes. These methods are based on either the irreversible cleavage of covalent bonds or the reversible opening and closing of rings. This paper overviews the fundamental mechanisms that govern the behavior of these photoresponsive systems, illustrates structural designs for fluorescence photoactivation, and provides representative examples of photoactivatable fluorophores in actions

Photoactivatable Synthetic Dyes for Fluorescence Imaging at the Nanoscale

The transition from conventional to photoactivatable fluorophores can bring the resolution of fluorescence images from the micrometer to the nanometer level. Indeed, fluorescence photoactivation can overcome the limitations that diffraction imposes on the resolution of optical microscopes. Specifically, distinct fluorophores positioned within the same subdiffraction volume can be resolved only if their emissions are activated independently at different intervals of time. Under these conditions, the sequential localization of multiple probes permits the reconstruction of images with a spatial resolution that is otherwise impossible to achieve with conventional fluorophores. The irreversible photolysis of protecting groups or the reversible transformations of photochromic compounds can be employed to control the emission of appropriate fluorescent chromophores and allow the implementation of these ingenious operating principles for superresolution imaging. Such molecular constructs enable the spatiotemporal control that is required to avoid diffraction and can become invaluable analytical tools for the optical visualization of biological specimens and nanostructured materials with unprecedented resolution

Intermolekular gekoppelte Bewegung in einem photochemisch gesteuerten System

Spannende Wendung: Eine molekulare Maschine wurde entworfen, bei der eine steuerbare Bewegung in einem Molekülteil in eine Drehbewegung eines gebundenen Gastmoleküls umgesetzt wird. Die Bestrahlung mit Licht löst im Wirtmolekül (bestehend aus einem Azobenzolchromophor, einem Ferrocenkomplex und zwei Zinkporphyrineinheiten) eine Bewegung ähnlich einer Schere aus, die eine Verdrehung des zweizähnigen Gastmoleküls bewirkt

Nanomaterials Synthesis and Applications: Molecule-Based Devices

The constituent components of conventional devices are carved out of larger materials relying on physical methods. This top-down approach to engineered building blocks becomes increasingly challenging as the dimensions of the target structures approach the nanoscale. Nature, on the other hand, relies on chemical strategies to assemble nanoscaled biomolecules. Small molecular building blocks are joined to produce nanostructures with defined geometries and specific functions. It is becoming apparent that natureʼs bottom-up approach to functional nanostructures can be mimicked to produce artificial molecules with nanoscaled dimensions and engineered properties. Indeed, examples of artificial nanohelices, nanotubes, and molecular motors are starting to be developed. Some of these fascinating chemical systems have intriguing electrochemical and photochemical properties that can be exploited to manipulate chemical, electrical, and optical signals at the molecular level. This tremendous opportunity has led to the development of the molecular equivalent of conventional logic gates. Simple logic operations, for example, can be reproduced with collections of molecules operating in solution. Most of these chemical systems, however, rely on bulk addressing to execute combinational and sequential logic operations. It is essential to devise methods to reproduce these useful functions in solid-state configurations and, eventually, with single molecules. These challenging objectives are stimulating the design of clever devices that interface small assemblies of organic molecules with macroscaled and nanoscaled electrodes. These strategies have already produced rudimentary examples of diodes, switches, and transistors based on functional molecular components. The rapid and continuous progress of this exploratory research will, we hope, lead to an entire generation of molecule-based devices that might ultimately find useful applications in a variety of fields, ranging from biomedical research to information technology

Molecule-Based Devices

The constituent components of conventional devices are carved out of larger materials relying on physical methods. This top-down approach to engineered building blocks becomes increasingly challenging as the dimensions of the target structures approach the nanoscale. Nature, on the other hand, assembles nanoscaled biomolecules relying on chemical strategies. Small molecular building blocks are joined to produce nanostructures with defined geometries and specific functions. It is becoming apparent that Nature's bottom-up approach to functional nanostructures can be mimicked to produce artificial molecules with nanoscaled dimensions and engineered properties. Indeed, examples of artificial nanohelicesnanohelix, nanotubesnanotube (NT) and molecular motors are starting to be developed. Some of these fascinating chemical systems have intriguing electrochemical and photochemical properties, which can be exploited to manipulate chemical, electrical and optical signals at the molecular level. This tremendous opportunity has led to the development of the molecular equivalent of conventional logic gates. Indeed, simple logic operations can be reproduced with collections of molecules operating in solution. Most of these chemical systems, however, rely on bulk addressing to execute combinational and sequential logic operations. It is essential to devise methods to reproduce these useful functions in solid-state configurations and, eventually, with single molecules. These challenging objectives are stimulating the design of clever devices that interface small assemblies of organic molecules with macroscaled and nanoscaled electrodes. These strategies have already produced rudimentary examples of diodes, switches and transistors based on functional molecular components. The rapid and continuous progress of this exploratory research will, hopefully, lead to an entire generation of molecule-based devices that might ultimately find useful applications in a variety of fields ranging from biomedical research to information technology