Search results for "Fluorescence"

Tristriazolotriazines: Luminescent Discotic Liquid Crystals

2018

Synthesis and Characterization of Fluorescent, Low-Symmetry Triphenylene Discotic Liquid Crystals:  Tailoring of Mesomorphic and Optical Properties

1996

A series of monofunctionalized triphenylene-based discotic liquid crystals were synthesized starting from 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene. These compounds are unique in that they possess a single electron-withdrawing group (and consequently a large dipole moment) connected directly to the polyaromatic core. All of the new liquid crystals show a significantly broader range of mesogenicity relative to the parent compound 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene. Moreover, some of the new mesogens exhibit a more ordered mesophase relative to the hexagonal columnar phase (Dh) at lower temperatures. Monofunctionalization of the triphenylene core has a dramatic effect on…

The effect of temperature on the internal dynamics of dansylated POPAM dendrimers

2011

The internal and rotational dynamics of the dansylated poly(propylene amine) dendrimers (POPAM) have been studied by time correlated single photon counting (TCSPC) and molecular dynamics (MD) simulations. The hydrodynamic volumes of the dendrimer generations from G1 to G4 were estimated by fluorescence anisotropy data. Experiments and simulations suggest that the volume and the shape of the dendrimers are temperature dependent. At low temperatures the dendrimer structure becomes more spacious and rigid and back-folding of the individual branches is slowed down. For the G3 and G4 generations the temperature effects are much stronger than for the smaller G1 and G2 generations, where back-fold…

Three-dimensional orientational colocalization of individual donor--acceptor pairs.

2004

We report on the determination of the three-dimensional orientation of the donor and acceptor transition dipoles in individual fluorescence resonance energy transfer (FRET) pairs by means of scanning optical microscopy with annular illumination. Knowledge of the mutual orientation of the donor and acceptor dipole is mandatory for reliable distance determination based on FRET efficiency measurements. In our model system perylenediimide as the donor and terryelenediimide as the acceptor are coupled via a stiff p-terphenyl linker. The absorption dipoles of the donor and acceptor are selectively addressed by the 488 nm and 647 line of an Ar/Kr mixed gas laser, respectively. A clear deviation fr…

In vivo molecular and morphological imaging by real time confocal mini-microscopy

2006

We evaluated a newly developed miniaturized confocal laser microscopy probe for real-time in vivo molecular and morphological imaging of normal, inflammatory, and malignant tissue in rodents. In the rigid mini-microscopy probe (diameter 7 mm), a single line laser delivers an excitation wavelength of 488 nm. Optical slice thickness is 7 μm, lateral resolution 0.7 μm. The range of the z-axis is 0 - 250 μm below the tissue surface. Organ systems were examined in vivo in rodent models of human diseases. FITC-labeled Lycopersion esculentum lectin was injected or selected cell populations stained for molecular targeting. Morphological imaging was performed using fluorescein sodium, FITC-labeled d…

Direct determination of minerals in human diets by infrared spectroscopy and X-ray fluorescence

2014

The use of near and mid infrared spectroscopy and X-ray fluorescence (XRF) to determine the concentration of mineral elements in Spanish human diets was investigated. Thirty-five commercial baby foods, 6 children fast food menus and 13 university canteen menu samples were analysed by infrared and XRF spectroscopy and spectra evaluated by using reference data obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES). Models for calcium, potassium, iron, magnesium, sodium and zinc determination were built and validated. Spectra were pre-treated by using different pre-processing algorithms (multiplicative scatter correction, standard normal variation, first derivate, ortho…

Comparison of Alkoxy-substituted 4,4´-Distyrylbiphenyls and the Corresponding 4,4´-Distyrylbenzenes

2008

Abstract Configurationally highly pure (E,E)-4,4´-bis(styryl)biphenyls 2a - e were obtained by Siegrist reactions of 4,4´-dimethylbiphenyl 3 and alkoxy-substituted benzaldimines (4a - e). DSC measurements have indicated different crystalline modifications of these conjugated compounds. The stilbenoid chromophores of 2a - e are compared to the stilbenoid chromophores in the OPV series, which have a similar length of conjugation. The intense fluorescence and the high transparency in the visible region are promising properties for an application of the donor-substituted compounds 2a - e in twophoton absorption (TPA) techniques.

Femtosecond Transient Absorption Study of the Dynamics of Acrylodan in Solution and Attached to Human Serum Albumin

2003

The excited-state relaxation dynamics of the protein-labeling dye acrylodan in solution and attached to human serum albumin has been studied by femtosecond transient absorption spectroscopy. Time-resolved spectra and kinetics of stimulated emission and excited-state absorption in the wavelength region from 400 to 800 nm were studied in ethanol and dimethylformamide. The excited-state solvation dynamics is characterized by multiexponential behavior in both solvents. In ethanol solution, the time dependence of the transient spectra is interpreted in terms of fast solvent relaxation followed by excited-state isomerization of the dye. Acrylodan attached to the protein shows a relaxation compone…

Some observations on the fluorometric determination of metallic elements in micellar media

1989

Abstract Experimental evidence is given allowing us to interpret why the detection limits obtained in micellar media are higher than those expected according to fluorescence enhancements for the niobium-lumogallion-tartrate system in the presence of different nonionic surfactants. The residual fluorescence of the surfactant solution and the competitive interaction with micelles between complexes and free ligands were studied. Near the critical micelle concentration of surfactants, remarkable changes in the emission spectra were observed in the case of both complex and free ligand solutions, which indicate the existence of interactions between the chemical system and surfactant monomers and …

Photophysical Properties of Oligo(phenylene ethynylene) Iridium(III) Complexes Functionalized with Metal-Anchoring Groups

2016

[EN] The electrochemical and photophysical properties of a family of conjugated ligands and their iridium(III) cyclometallated complexes are described. They consist of a series of monocationic Ir-III bis-2-phenylpyridine complexes with p-phenylethynyl-1,10-phenanthroline ligands of different length. The structure of these ligands includes terminal acetylthiol or pyridine groups, which can provide good electrical contacts between metal electrodes. Cyclic voltammetry, absorption and emission spectroscopy, laser flash photolysis and density functional theory calculations reveal that the high conjugation of the diimine ligand affords small energy gaps between the frontier orbitals. Nevertheless…