Effect of Structural Rigidity

Finally, this description of photofluidity as a summative bondbreaking process emphasizes the importance of quantum efficiency during the irradiation process. In particular, much precaution must be taken in ensuring that all glasses are irradiated at an individual 

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Figure 9.11(b). Effect of structural rigidity on quantum yield, 4>F... 

The effect of structural rigidity was also demonstrated quantitatively on a series of As-S glasses exposed to different dosages of °Co radiation [40]. Figure 2.19a shows the enthalpy release A//of glasses exposed to cumulative doses of 3 MGy and 4 MGy compared to that of unexposed glasses. All samples had been stored in the dark at room temperature for 38 months prior to irradiation. 

The effect of structure (linear or branched, incorporation of heteroatoms, etc.) and conformational flexibility or rigidity of the fluorous ponytail on the partition coefficients has not yet been studied in detail. 

The absolute moleeular weights of these materials have been established by GPG by means of the universal calibration technique that involves the acquisition of intrinsic viscosity data. As with the aforementioned platinum polyyne polymers 166 (M = Pt(P"Bu3)2 x = Z), the intrinsic viscosities were found to be independent of the nature of the solvent and a Mark-Houwink a-value of 1.5 was determined, which is indicative of a rodlike structure. Interestingly, it was found that in this case, GPG, using PS standards, underestimates the true molecular weight of the polymers. This was attributed to the high molar mass of a repeat unit in the Ni polymer 207 compared to PS, which overcompensates for the effect of the rigid-rod structure that would be expected to lead to the opposite situation. Absolute values of of up to ca. 1 x 10 were determined for the polymer samples. 

To discuss the effect of structural ordering of the polymer on selectivity, we have been focusing on secondary structures of poly(o -amino acid)s, i.e., polypeptides.They provide rigid and exact conformations, such as a-helix and 3-structure, spontaneously if polymerization is done with a purely chiral amino acid. The poly(L-alanine), poly(L-leucine), and poly(L-phenylalanine) with a terminal reactive trimethoxysilyl group can be prepared by the corresponding iV-carbox-yanhydrides and 3-aminopropyltrimethoxysilane as an initiator for polymerization. However, in this case, a... 

In conclusion, the presence of detectable CT fluorescence for 9(8), 14(8), 15(8) and 16(8) allowed us to evaluate directly the effect of structural modifrcations leading to a change in orbital symmetry, on the electronic coupling relevant for charge recombination. The results indicate that in the present type of rigidly bridged systems orbital symmetry... 

With that idea, in 1958, Overberger s group undertook a program of research to study the factors contributing to the formation of preferred conformation of optically active polyamides. The synthesis and optical properties of a series of asymmetric polyamides with different degrees of structural rigidity imposed on the polymer chain, and generally also their models, have been reviewed by these authors in 1969 [49] and also by Pino [2] in 1970. The conformational aspect is treated in this book in detail, by Dr Montaudo and Dr P. Finocchiaro, and chiroptical effects independent of conformation by Dr Vert (XXI). 

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