106 research outputs found
Influence of monolayer state on spectroscopy and photoisomerization of an amphiphilic styryl-pyridinium dye on a solid substrate
No full textThe spectroscopy and photochromic properties of transferred monolayers of the amphiphilic styryl-pyridinium dye 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate (DMPOP) were studied at different conditions during their transfer. The emission maxima of the monolayers transferred from the air-water interface in the liquid-expanded phase are strongly dependent on the surface pressure applied during the transfer process, even at values when the area per molecule is 2-3 times larger than the area occupied by a chromophore. In monolayers transferred from the liquid-condensed phase, the presence of a different kind of aggregates was observed. The fluorescence emission properties of the monolayers can be reversibly modulated by photoinduced E-Z isomerization. A blue shift up to 72 nm in the emission maximum, depending on the transfer conditions of the films, can be obtained by irradiation with blue light, and partially recovered (a red shift of up to 26 nm) with UV radiation. The rate at which the first process (E -> Z) takes place is drastically reduced in monolayers transferred from the liquid-condensed phase as compared to those transferred from the liquid-expanded one. However, the rate of the reverse reaction (Z -> E) is not significantly altered. These properties make DMPOP a promising material for the preparation of Langmuir-Blodgett films, whose properties can be effectively controlled by the transfer conditions and subsequently optically modulated, for potential applications as photonics devices for data storage
Molecular organization of an amphiphilic styryl pyridinium dye in monolayers at the air/water interface in the presence of various anions
No full textAmphiphilic 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate and bromide form stable monolayers at the air/water interface. Small differences in the surface pressure-area and Surface potential-area isotherms depending on the anion indicate interactions between the chromophore and the anions on the pure water subphase. The monolayer behavior is considerably modified on 10 mM aqueous solutions of KI, KClO4, KCl, and KF as revealed by isotherm measurements, reflection spectroscopy, and Brewster angle microscopy. The phase transition observed in the isotherms is shifted to higher surface pressure because of variation of the salt according to the Hofmeister series. Upon monolayer compression, the chromophores are increasingly tilted, and a shift of the band to longer wavelengths is attributed to the environment becoming less polar. However, in the case of KCl at small areas per molecule, relaxation is observed at constant area with the appearance of a new band shifted to shorter wavelengths. This band is assigned to small associates of about four chromophores (H aggregates). In the case of KI, a new band shifted to longer wavelengths is found. Theoretical calculations did not yield a transition in the observed range, even for large aggregates (J aggregates). Therefore, other interactions may be responsible for the appearance of this band
Spectroscopic properties of an amphiphilic styryl pyridinium dye in Langmuir-Blodgett films
No full textSurface pressure-molecular area and surface potential-molecular area isotherms of the recently synthesized amphiphilic dye 1 indicate that it forms monolayers on distilled water. A shift of the fluorescence maximum from 505 up to 570 nm was measured upon increasing the surface pressure applied during the Langmuir-Blodgett transfer from 7 up to 20 mN/m, and a slight red shift in the absorption. The increase of the surface pressure also produces a new blue-shifted band only present in the p-polarized component of the absorption spectra under oblique incidence of light. The results were interpreted as reorientation and association of the chromophores in the monolayer, according to the extended dipole model
Triplet-Triplet Annihilation Assisted Upconversion: All-Optical Tools for Probing Physical Parameter of Soft Matter
No full textBright constant color upconversion based on dual 980 and 1550 nm excitation of SrF2:Yb3+, Er3+ and β-NaYF4:Yb3+, Er3+ micropowders― considerations for persistence of vision displays
No full textUpconversion phosphors are of interest for 2D head-up and 3D volumetric displays. These exploit persistence of vision; fast scanning of the near-infrared excitation means that the material at each emission point is only excited for a short fraction of the time it takes to trace the whole image. To achieve an average luminance on the order of 100 cd m−2 (necessary for the display to be visible in ambient indoor lighting), the luminance during excitation must be several orders of magnitude higher than its time-averaged value. For this purpose, efficient energy-transfer upconversion materials such as the benchmark β-NaYF4:Yb3+,Er3+ are of obvious interest. However, under 980 nm excitation the perceived color of their emission varies with their luminance, limiting their applicability for a grayscale display. We demonstrate that under dual 980 nm and 1550 nm excitation, a constant green color can be maintained at CIE coordinates (0.31, 0.66), as the luminance is varied. At moderate power densities of 100 W cm-2 at each excitation wavelength, a luminance of 8 × 106 cd m−2 can be achieved. Conservatively considering that the luminance will be reduced by 5 orders of magnitude in a laser scanning display, this material will still be bright enough to be viewed in indoor ambient light. We also investigate SrF2:Yb3+,Er3+, and find color tuning from the red to green is possible under dual wavelength excitation, but only at limited luminance, so color tuning in this manner would only be appropriate for displays viewed in a dark environment
Micellar carrier for triplet–triplet annihilation-assisted photon energy upconversion in a water environment
No full textFabrication of Polymer Ellipsoids by the Electrospinning of Swollen Nanoparticles
No full textElectrospinning is used to deform originally spherical
polymer
nanoparticles into ellipsoidal nanoparticles. The polymer nanoparticles
are swollen and the dispersion is then electrospun. Under certain
conditions, the stretching generated in the electrospinning jet is
enough to generate elongated nanoparticles embedded in fibers. The
formation of the anisotropic particles is observed by stimulated emission
depletion (STED) microscopy performed on fluorescent nanoparticles
and by electron microscopy measurements on the nanoparticles recovered
after removal of the fiber matrix
Enhanced photocatalytic efficiency via improved contact in a solar-driven membrane reactor for steroid hormone removal
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