Absorption spectra distortions

Jin et al. [487] synthesized and studied the PL and EL properties of polymers 403 and 404 that differ by the position of the alkoxy substituent in the phenyl ring, expecting different distortion of the polymer main chain (and consequently conjugation length) due to different steric factors for para- and ort/zo-substitution (Chart 2.98). The absorption spectrum of the ortho-polymer 403 showed a substantial blue shift of 40 nm compared to para 404 and a decrease in EL turn-on voltage (4.5 and 6.5 V, respectively). Both polymers demonstrated nearly the same PL and EL maxima (Table 2.1). 

Figure 8.2 presents the fluorescence of pyrene on silica gel. The loading is low so that pyrene is predominantly adsorbed as nonaggregated monomers (Mi). The backward fluorescence spectrum Fb of this sample is very comparable to the spectrum in polar solvents and not distorted by reabsorption. However, the forward spectrum Ft is almost completely suppressed in the region of overlap with the o -transition and hot sidebands of the weak first absorption band Si. The absorption coefficients of the sample vary widely from k" = 0.1 cm 1 (Si-band, Aa = 350-370 nm) to k = 25 cm-1 (S2-band, 1 290-340 nm), and in a first approximation the excitation spectrum of Fh reflects this variation correctly (Figure 8.2, left). The Ff-excitation spectrum, however, has only little in common with the real absorption spectrum of the sample. 

AS = 13 e.u. for the Cu-template resin, and AH = -0.8, AS = 9,8 (K - 540) for the resin synthesized without any template ion. The larger change in entropy observed in the complexation of the Cu-template resin indicated that die Cu-template resin selectively adsorbed Cu ions by entropic effect. Furthermore, the absorption spectrum of the Cu complex of the Cu template resin was located at a wavelength 10—20 nm shorter than those of the other resins70 and the ESR parameters of the Cu complex of the Cu-template resin were similar to those of the non-distorted planar Cu complex71. From these results, it was suggested that the conformation of the polymer-ligand chain in the Cu template resin remained the best one for the Cu ion. 

Fig. 17. Delayed fluorescence spectrum of 5 X 10-63/ anthracene in ethanol.84 Half-bandwidth of analyzing monochromator was 0.05 ju-1 at 2.5 n K Intensity of exciting light was approximately 1.4 X 10 einstein cm. a sec.-1 at 2.73m-1 (366 mju). (1) Normal fluorescence spectrum (distorted by self-absorption). (2) Delayed emission spectrum at sensitivity 260 times greater than for curve 1. (3) Spectral sensitivity of instrument (units of quanta and frequency).

It is called trivial because it does not require any energetic interaction between the donor and the acceptor. It is merely reabsorption of fluorescence radiation in accordance with Beer s Law and shows r 2 dependence on donor-acceptor distance. Although called trivial, it causes radiation imprisonment and can be important factor to be considered in fluorescence measurements. It may introduce error and distort emission spectrum by absorbing only that portion which overlaps its absorption spectrum. It is specially troublesome in studies on concentration quenching. 

The absorption spectrum and first formation constant of [Cr(bipy)]2+ have been determined spectrophotometrically in hexamethylphosphoramide (HMPA) (see also Table 39). Since log Ki (4.61) is slightly larger in HMPA than in water, it is said that [Cr(bipy)(HMPA)2]2+ is tetrahedral, although from the general chemistry of chromium(Q) the ion would be expetrted to be in planar or distorted octahedral coordination.52... 

The absorption spectrum of the bare Cu Y zeolite was also measured and interpreted using a model of a CuII-0(Sl ) site. The 0-CuII-0 angle was determined to be 117° from optical spectra, in excellent agreement with 115.9° found by X-ray crystallography (20). Based upon the observed spectral splitting of 1800 cm- of the states of Cu -, first order vibronic theory predicted a Jahn-Teller distortion of 0.05-0.06 A along the Cu11- bonds. 

The acidic fraction, which adsorbs to the resin and must be eluted by acidic extraction, exhibits a different infrared absorption spectrum in the 6-7 micron range. Sharp bands at 6.3 and 6.6 microns indicate absorption assigned to distortion of the aromatic nuclei occurring in lignin breakdown products. 

Fig. 7.1. Spectral characteristics of the (=Si-0)3Si-N = N-O radical, (a) EPR spectrum (the central component of the spectrum at 300 K is distorted by the superposition of the admixed signal and is not shown (b) optical absorption spectrum (c) IR spectrum (calculated form of two normal vibrations of the radical F3Si-N = N-O are shown).

The crystal structures of transition metal compounds and minerals have either cubic or lower symmetries. The cations may occur in regular octahedral (or tetrahedral) sites or be present in distorted coordination polyhedra in the crystal structures. When cations are located in low-symmetry coordination environments in non-cubic minerals, different absorption spectrum profiles may result when linearly polarized light is transmitted through single crystals of the anisotropic phases. Such polarization dependence of absorption bands is illustrated by the spectra ofFe2+ in gillespite (fig. 3.3) and of Fe3+in yellow sapphire (fig. 3.16). 

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