Polymer molecule, electronic states excitation

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

Alternatively, the electron, or the polymer anion, may react with an existing cation radical producing an excited state of the polymer molecule, P. For example. 

The second reason for delocalization of energy losses is the collective nature of excited states. This collectivity may exist even for excited electronic states of a single molecule. The simplest example is the excitation of zr-electron states, which are delocalized along the molecule. When a fast electron excites such a molecule, it transfers its energy to the whole ensemble of tt electrons. As a result, the energy absorption is delocalized along the molecule, and the latter can be a long (e.g., a polymer molecule). 

Because of periodic symmetry, the electronic excitation states in a molecular crystal are also of collective nature. These are the well-studied exciton states.81 82 Their energy is close to that of discrete electronic states of isolated molecules (4-8 eV), but the excitation envelops a large group of molecules, migrating efficiently up to 100 nm along the crystal.82 In the same manner, because of efficient migration, the excitation of a fragment of a polymer chain rapidly spreads over the whole molecule.37... 

Thus, the excitation of discrete electronic states (AEn < /,) in polymer molecules and molecular crystals is certainly delocalized. 

Lindsay, G. A. and Singer, K. D. (eds) (1995). Polymers for Second-Order Nonlinear Optics. ACS Symposium Series. American Chemical Society, Washington, DC Liptay, W. (1969). Angew. Chem. 81, 195 Angew. Chem. Int. Ed. Engl. 8, 177 Liptay, W. (1974). Excited States, Vol. 1. Dipole Moments and Polarizabilities of Molecules in Excited Electronic States (ed. E. C. Lim). Academic Press, New York, p. 129... 

The linear optical properties of the isomers of 4-[ethyl(2-hydroxy-ethyl) aminoj-4-nitrobenzene (disperse red 1 or DRl) have attracted the attention of researchers for many years, and during the last decade, the nonlinear optical properties of DRl placed in a polymer environment also have been of interest. The trans- and as-isomers of DRl are illustrated in Figure 9.1. Tlie photoisomerization reaction begins by elevating molecules to excited electronic states, followed by nonradiative decay back to the ground slate in either the cis or trans forms, as illustrated in Figure 9.2. TTie ratio of dsUrans states is dependent on the quantum yield of the appropriate photoisomerization reaction (e.g., and for the direct trans= cis and reverse cis= trans photoisomerization reactions, respectively). As the trans-isomer is more stable than the c/s-isomer, molecules in the cis form convert to the trans form bv... 

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