Transiciones térmicas en recubrimientos polisiloxánicos de fibras de vidrio

Se realizó una estimación de las temperaturas de relajación de recubrimientos poliméricos en fibras de vidrio. Para ello, se llevó a cabo el seguimiento de la respuesta fluorescente, en función de la temperatura, de dos fluoróforos químicamente enlazados al recubrimiento polimérico. Las fibras de vidrio fueron tratadas con una disolución acuosa de 3-aminopropiltrietoxisilano(APES), y una mezcla al 50 % de APES y de 3-aminopropilmetildietoxisilano (APDES). Los marcadores fluorescentes, cloruro de pireno-1-sulfonilo (PSC) y cloruro de 1-dimetilamino-5-naftalenosulfonilo (DNS), se anclaron a las fibras de vidrio silanizadas a través de la formación de un compuesto sulfonamida estable y fluorescente (PSA y DNSA respectivamente).Se realizaron sus espectros de emisión en función de la temperatura en el intervalo (133, 413)K. Los resultados mostraron transiciones térmicas a bajas temperaturas para las muestras estudiadas indicando la alta flexibilidad de la región de acoplamiento. Además, dicha temperatura de transición depende de forma clara de la estructura del polímero que recubre a las fibras.It was estimated the relaxation temperatures of polymeric coatings on glass fibers. In order to do this, it was carried out the fluorescent response study, as a function of temperature, of two dyes chemically bonded to the polymeric coating. The glass fibers were treated with aqueous solutions of 3-aminopropyltriethoxisilane (APES) and a 50 % mixture of APES and 3-aminopropylmethyldiethoxisilane (APDES). The fluorescent labels, pyrene-1-sulfonyl chloride (PSC) and 1-dimethylamino-5- naphtalenesulfonyl chloride (DNS), were attached to the silanized glass fibers by the formation of a stable and highly fluorescent sulfonamide conjugate (PSA and DNSA respectively). Emission spectra were recorded as a function of temperature in the range (133, 413)K. The results shown thermal transitions at low temperatures, which reflect the high flexibility of the coupling region. In addition, that transition temperature clearly depends on the structure of the polymeric coating of the glass fibers

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

A comprehensive photophysical and spectroscopic study of a new class of p-phenylenevinylene oligomers (PPV-trimers) possessing different alkyl and alkyloxy sidechain substituents and different end groups (aldehyde, CC, phenylene and anthracene units) was undertaken in solution at room temperature (293 K), low temperature (77 K) and in thin films. The study comprises absorption, emission and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and lifetimes. The data allow the determination of rate constants for all decay processes. From these, several conclusions could be drawn. Changing from alkyl to alkyloxy substituents does not change fluorescence and internal conversion yields but decreases the (already small) intersystem crossing yield. The introduction of anthracene at the terminal ends of the PPV-trimers leads to the lowest fluorescence yield reported in this study. Of particular importance is the fact that the fluorescence quantum yields in films are of the same order of magnitude as those in solution, which suggests the potential for use of these oligomers for light-emitting device applications. With one of the alkyloxy derivatives, a more detailed study of the early part of the fluorescence decay was made, and it was found that upon excitation a fast conformational relaxation process of the initially excited oligomer occurs, leading to a more planar conjugation segment.http://www.sciencedirect.com/science/article/B6TFM-4KXWDH3-1/1/7fda7eda4dc250233a3c905cd185f89