Polycrystalline aromatic

Radicals and radical ions, formed on /-radiolysis of several polycrystalline aromatic carboxylic acids containing a thioether group in various positions with respect to the aromatic ring and to the carboxylic function, were identified using the electron spin resonance technique at 77 K and on subsequent warming over the temperature range of 95-293... 

The influence of the metal on electrosorption was also considered in the adsorption of aromatic compounds. Extensive studies of adsorption of different aliphatic and aromatic compounds on a polycrystalline Pt electrode in O.OIMHCI solution were done by Bockris etal. Using different techniques (radiotracer, FTIR, and ellipsometry), they were found that aromatic molecules are adsorbed parallely to the electrode surface and that the potential dependence of adsorption is symmetrical around the pzc. It was concluded that the dependence of adsorption on the potential is mostly determined by the interaction of water with the Pt surface. 

Crystals of DGEBA monomer were prepared. The polycrystalline powder was run at different temperatures. There was no coalescence of the aromatic peaks. 

Perhaps the simplest optically controlled switches are single molecules embedded in a solid host matrix. These systems consist of an amorphous, polycrystalline, or crystalline film doped with dilute concentrations of impurity molecules. The most commonly used dopant molecules are fused polycyclic aromatic hydrocarbons and porphyrins. In addition to facile sample preparation, these planar molecules absorb in the visible to near IR regions of the spectrum, possess large extinction coefficients in both the ground and excited states, and have high fluorescence quantum yields. 

The vibrationally excited singlet Si and triplet Tf, expected upon the annihilation of the lowest excited triplets Ti, have an energy below the autoionization threshold of typical aromatic crystals [26], thus, no intrinsic photoionization has been observed in these solids. However, the presence of intentional or non-intentional admixtures can allow the triplet-triplet interaction-induced photoionization forming a free carrier in the matrix and a trapped carrier on an admixture molecule. Also, such a process has been reported for the CT triplet states localized on the donor molecule, e.g. in polycrystalline samples of CT complex anthracene-tetracyanoben-zene, where the triplets are localized on the anthracene donor (3Di). Annihilation of 3Di results in the population of non-relaxed excited states of the complex 1(D+A ) and 3(D+A") , dissociation of which may lead to the formation of free charges D+ [214]. 

Early studies with smooth polycrystalline Pt electrodes indicated that aromatic compounds such as / -diphenols... 

P, As) in which the aromatic molecules occur in stacks this situation results in metal-like electrical conductivity (a) (a = 0.12 0.046 ft-1 cm-1 for a polycrystalline pellet). This finding suggested the possibility of analogous behavior in the fluoroaromatic series. Materials containing dimeric cations, however, have not been isolated from reaction mixtures containing excess amounts of the neutral monomers or from controlled reduction of monocation salts. In each case, the cations are monomeric and magnetically independent of one another. 

The chemical shift anisotropy arises from the nonspherical electron density around the nuclei, and is particularly prominent for aromatic and carbonyl (C=0) carbon types. These carbon types experience different shieldings of the magnetic field depending on whether the bond axes are parallel or perpendicular to the external magnetic field. For polycrystalline or amorphous materials all orientations are possible, including these two extremes. 

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