Solid-state quenching

Co-free PAE). In PAE-CoCpl, the fluorescence quantum yield is only 18% of that observed for Co-free PAE, even though the quencher substitutes less than 0.1% of the aryleneethynylene units. The fluorescence in solution disappeared in PAE-CoCp4, where every fifth unit is a cyclobutadiene complex. The mechanism by which this quenching occurs is via the cobalt-centered MLCT states [82,83], conferred onto the polymer by the presence of cyclobutadiene complexes. Even in the solid state the polymers PAE-CoCpl-2 are nonemissive. It was therefore shown that incorporation of CpCo-stabilized cyclobutadiene complexes into PPEs even in small amounts leads to an efficient quenching of fluorescence in solution and in the solid state. Quenching occurs by inter- and intramolecular energy transfer [84]. 

Curiously, however, the results of curve a are not reproducible on repeated runs (curve c). Curves similar to curve c were also obtained for naphthalene - and naphthalene - mixed crystals. Probably A and naphthalene crystallize out separately, depending upon subtle variations of experimental conditions for evaporation of the ether solvent. This demonstrates possible complexities In doing solid-state quenching experiments by our method (section 4). 

The simplest form of melt extmsion is the use of a slot die to form the molten polymer into a thin flat profile which is then quenched immediately to a solid state (Fig. 1). This is usually done by contacting the hot web very quickly on a chilled roU or dmm. A liquid quenching bath may be used ia place of or contiguous to the chill roU. Depending on the polymer type or formulation, the quenched web is generally substantially amorphous. In some cases, the web may be drawn down ia thickness by overdriving the quenching roU relative to the extmsion velocity. 

In order to address the possible influence of positional disorder, we have chosen to analyze the way basic operations such as translations and rotations affect the properties calculated for highly symmetric configurations. This approach could provide guidelines to prevent the loss of significant optical coupling between the ground state and the lowest excited state, and hence the quenching of luminescence in the solid state. 

Risbud, S. H., Kirkpatrick, R. J., Taglialavore, A. P. Montez, B. (1987). Solid-state NMR evidence of 4-, 5- and 6-fold aluminium sites in roller-quenched SiOj-Alj O3 glasses. Journal of the American Ceramic Society, 70, ClO-12. 

State decarbonylation reaction in total synthesis was reported recently in the case of natnral prodnct (+)-herbetenolide, which farther illustrates the exquisite control that the solid state may exert on the chemical behavior of the otherwise highly promiscuous reactive intermediates. As word or caution, it should be mentioned that intramolecular quenching effects known to act in solution can also affect that reaction in the solid state. Recently reported examples include the well-known intramolecular P-phenyl and electron transfer quenching. ... 

Both polyethylene terephthalate and polybutylene terephthalate exhibit partial crystallinity in the solid state. The molecular weight of the polymer and the time permitted for cooling define the degree of crystallinity of the polymer. Very slow cooling results in high crystallinity and opacity, while fast quenching creates low crystallinity, high clarity material. 

Sinha, A. K., Giessen, B. C., and Polk, D. E., Metastable Phases Prodiced by Rapid Quenching from the Vapor and the Liquid. Treatise on Solid State Chemistry, ed. N. B. Hannay. Vol. 3. 1976. 

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