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Fluorescence Modulation (fluorescence + modulation)

Distribution by Scientific Domains
Polymers and Materials Science66%

Selected Abstracts

Fluorescence Modulation in Polymer Bilayers Containing Fluorescent and Photochromic Dopants,

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005
M. Tomasulo
Abstract We have identified viable operating principles for the modulation of optical signals under the influence of optical stimulations. They are based on the overlap between the emission bands of a fluorescent compound and the absorption bands of one of the two forms of a bistable photochromic switch. Under these conditions, the photoinduced interconversion of the two states of the photochrome modulates efficiently the emission intensity of the fluorophore. We have implemented this mechanism for intermolecular fluorescence modulation with multilayer structures. They consist of two quartz plates sandwiching two overlapping polymer layers. One of the polymers is doped with a fluorescent benzofurazan. The other contains a photochromic spiropyran. The multilayer assembly is operated with two light sources. One of them is centered at the excitation wavelength of the fluorophore, where neither of the two states of the photochrome absorbs. The other light source is switched between ultraviolet and visible wavelengths to induce the interconversion between the two states of the photochrome. The light emitted by the fluorescent component has to propagate through the photochromic layer before reaching a detector. It can do so efficiently for only one of the two states of the photochrome. It follows that a measurement of the light intensity reaching the detector can read the state of the photochromic switch, which in turn is written and erased with optical stimulations. Thus, our strategy for all-optical processing can be used to store and retrieve binary digits, as well as to implement optical inversion, with the aid of engineered molecule-based components. [source]

A High-Content Diarylethene Photochromic Polymer for an Efficient Fluorescence Modulation

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2006
Yong-Chul Jeong
Abstract Summary: A highly fluorescent photochromic polymer, poly-BTFO4, was prepared. The fluorescence quantum yield of the poly-BTFO4 was six times higher than that of BTFO4. Fatigue resistance of the polymer at its photostationary state was significantly enhanced compared with that of BTFO4. Importantly, the poly-BTFO4 film also showed an efficient photochromism as well as strong fluorescence similar to the results in solution, which allow photoinduced fluorescence switching applicable to optical switches. Improvement of fluorescence quantum yield and fatigue resistance. [source]

A Combination of Selective Light Reflection and Fluorescence Modulation in a Cholesteric Polymer Matrix

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 3 2005
Dasha Medvedeva
Abstract Summary: The phase behavior and optical properties of a cholesteric ternary copolymer, containing nematogenic phenylbenzoate, cholesteric, and photochromic diarylethene side groups, and its mixture with 2 wt.-% fluorescent dopant were studied. The investigation of the kinetics of a photochemical opening-cycle process of the photochromic groups in the cholesteric mixture proved the energy transfer from the fluorescent dopant to the photochromic diarylethene groups. It was shown that the fluorescence intensity of the fluorescent dopant could be controlled by the portion of the "closed" form of the diarylethene groups. During the photocyclization of the photochromic groups a "degeneration" of the selective light reflection of the cholesteric matrix is observed. Fluorescence-resonance energy transfer makes possible the process of photosensitization of the back ring-opening photoreaction of the photochromic diarylethene groups in the cholesteric polymer matrix. [source]

Identifying the Bond Responsible for the Fluorescence Modulation in an Amyloid Fibril Sensor

CHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2010
Anvita Srivastava
Abstract An ultrafast intramolecular bond twisting process is known to be the responsible mechanism for the sensing activity of the extensively used amyloid fibril sensor thioflavin,T (ThT). However, it is not yet known which one of the two possible single bonds in ThT is actually involved in the twisting process. To resolve this fundamental issue, two derivatives of ThT have been designed and synthesized and subsequently their photophysical properties have been studied in different solvents. It is understood from the present study that the rotation around the central CC single bond, and not that around the CN single bond, is primarily responsible for the sensor activity of ThT. Detailed viscosity-dependent fluorescence studies revealed that the ThT derivative with restricted CN bond rotation acts as a better sensor than the derivative with free CN bond rotation. The better sensory activity is directly correlated with a shorter excited-state lifetime. Results obtained from the photophysical studies of the ThT derivatives have also been supported by the results obtained from quantum chemical calculations. [source]

Fluorescence Modulation in Polymer Bilayers Containing Fluorescent and Photochromic Dopants,

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005
M. Tomasulo
Abstract We have identified viable operating principles for the modulation of optical signals under the influence of optical stimulations. They are based on the overlap between the emission bands of a fluorescent compound and the absorption bands of one of the two forms of a bistable photochromic switch. Under these conditions, the photoinduced interconversion of the two states of the photochrome modulates efficiently the emission intensity of the fluorophore. We have implemented this mechanism for intermolecular fluorescence modulation with multilayer structures. They consist of two quartz plates sandwiching two overlapping polymer layers. One of the polymers is doped with a fluorescent benzofurazan. The other contains a photochromic spiropyran. The multilayer assembly is operated with two light sources. One of them is centered at the excitation wavelength of the fluorophore, where neither of the two states of the photochrome absorbs. The other light source is switched between ultraviolet and visible wavelengths to induce the interconversion between the two states of the photochrome. The light emitted by the fluorescent component has to propagate through the photochromic layer before reaching a detector. It can do so efficiently for only one of the two states of the photochrome. It follows that a measurement of the light intensity reaching the detector can read the state of the photochromic switch, which in turn is written and erased with optical stimulations. Thus, our strategy for all-optical processing can be used to store and retrieve binary digits, as well as to implement optical inversion, with the aid of engineered molecule-based components. [source]

Bisthienylethenes Containing a Benzothiadiazole Unit as a Bridge: Photochromic Performance Dependence on Substitution Position

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010
Weihong Zhu Prof.
Abstract A conveniently synthesized photochromic compound, BTB-1, containing an unprecedented six-membered 2,1,3-benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB-1 can be modulated by solvato- and photochromism. However, the analogue BTB-2, in which the dimethylthiophene substituents are relocated to the 5,6-positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six-membered bridge bisthienylethenes (BTEs) in which the photochromism can be controlled by the substitution position. The photochromism difference is elucidated by the analysis of resonance structure, the Woodward,Hoffmann rule, and theoretical calculations on the ground-state potential-energy surface. In a well-ordered single-crystal state, BTB-1 adopts a relatively rare parallel conformation, and forms an interesting two-dimensional structure due to the presence of multiple directional intermolecular interactions, including CH,,,N and CH,,,S hydrogen-bonding interactions, and ,,, stacking interactions. This work contributes to several aspects for developing novel photochromic BTE systems with fluorescence modulation and performances controlled by substitution position in different states (solution, organogel, and single crystal). [source]