Fiber, absorption spectra

A supramolecular assembly of macromolecules bearing antenna dendron has been reported. Pyrazole-anchored PBE dendrons were synthesized to examine the coordination behavior to transition-metal cations (Cu, Au, Ag) [31]. Self-assembled metallacycles were found. The Cu-metallacycle further formed luminescent fibers about 1 pm in diameter. The luminescence (605 nm) occurred by the excitation of the dendron (280 nm) and the excitation spectrum was coincident with the absorption spectrum of the dendron, suggesting the antenna effect. Interestingly, the luminescence of the Cu-metallacycle fiber disappeared when the fiber was dissociated into the individual metallacycles in C2H2. 

Measuring U-v - spectrum displayed, that modifier concentration of 2% to the mass of a fiber change spectrum considerably. It is necessary to note, that after irradiation the spectrum looks differently absorption bands change to reduction. Possibly, these changes are caused by absorption of CDA decomposition products CDA, which, in its turn, decelerates further polymer decomposition. 

The interest in Er -doped fibers stems from the fact that silica as well as fluoride glasses show very low absorption in the emission region mentioned above (see Fig. 10.19). The silica glasses transmit the / j/2 -> /15/2 emission best the fluoride glasses the /,i/2 -> /i3/2 emission. Figure 10.19 is an absorption spectrum for... 

Energy transfer fibers are based on the principle that, upon excitation, a donor molecule wUl transfer a portion of its energy to an acceptor molecule if there is overlap between the donor s emission and the acceptor s absorption spectrum. This transfer occurs without the emission of a photon and is primarily the result of a dipole-dipole Interaction between the donor and acceptor. The efficiency of singlet dlpde-dipoie energy transfer is predicted by Forster theory (27). 

The sample techniques just described are designed for collection of transmission (absorption) spectra. This had been the most common type of IR spectroscopy, but it was limited in its applications. There are many types of samples that are not suited to the conventional sample cells and techniques just discussed. Thick, opaque solid samples, paints, coatings, fibers, polymers, aqueous solutions, samples that cannot be destroyed such as artwork or forensic evidence samples, and hot gases from smokestacks—these materials posed problems for the analytical chemist who wanted to obtain an IR absorption spectrum. The use of reflectance techniques provides a nondestructive method for obtaining IR spectral information from materials that are opaque, insoluble, or cannot be placed into conventional sample cells. In addition, IR emission from heated samples can be used to characterize certain types of samples and even measure remote sources such as smokestacks. In reflectance and emission, the FTIR spectrometer system is the same as that for transmission. For reflectance, the sampling accessories are different and in some specialized cases contain an integral detector. The heated sample itself provides the light for emission measurements therefore, there is no need for an IR source. There may be a heated sample holder for laboratory emission measurements. 

Optical fiber detectors are usually utilized as ether miniature spectrophotometers or fluorimeters, because of the availability of indicator dyes that can be detected by absorbance or fluorescence methods. Figure 12 shows the absorption spectrum for phenol red, a dye commonly used as pH indicator. By measuring the absorption of solutions of phenol red at two wavelengths, the isobestic point where absorption is virtually independent of pH and at 600 m u where the intensity of absorption is very pH sensitive, one... 

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