Polygermanes electronic properties

Recent studies of polymeric Group IV catenates (in particular, polysilanes and polygermanes, la,b have demonstrated that there is significant sigma electronic delocalization along the polymer backbone which is responsible for many of the curious electronic properties of this class of materials [3]. 

The polysilanes can be regarded as one-dimensional analogs to elemental silicon, on which, of course, nearly all of modem electronics is based. The photophysical behavior of polysilanes is not approached by any other materials, save for the less stable and more costly polygermanes and polystannanes. The remarkable properties of polysilanes have led to intense interest, and to numerous proposed high-tech applications. But the great promise of polysilanes as materials has yet to be realized. Their only commercial use at present is as precursors to silicon carbide ceramics, an application which takes no advantage of their optical or electronic properties. 

Since the electronic absorption spectra of polvsilanes and polygermanes also depend strongly on conformation (3), these materials provide a unique opportunity to study the effect of backbone conformation on the NLO properties, particularly since varying alkyl substituents can dramatically influence the backbone structure through intermolecular interactions (e.g., side chain crystallization) while causing... 

As explained in the introduction, the polysilanes (and related polygermanes and poly-stannanes) are different from all other high polymers, in that they exhibit sigma-electron delocalization. This phenomenon leads to special physical properties strong electronic absorption, conductivity, photoconductivity, photosensitivity, and so on, which are crucial for many of the technological applications of polysilanes. Other polymers, such as polyacetylene and polythiophene, display electron delocalization, but in these materials the delocalization involves pi-electrons. 

US6S. Both polygermanes and polystannanes may find applications because of their unique optical, electronic, and chemical properties. Some of these potential uses include photoresist layers (44,59,60), third-order nonlinear optical materials (50), charge transport polymers (61,62), photoconductors, microlitho-graphic materials (63), and photoinitiators (59). 

The optoelectronic properties result from 0-0 delocalization and confinement of the conjugated electrons along the backbone. Polygermanes resemble polysilanes in this regard. The latter have been studied in more detail. Polysilanes exhibit UV absorption " and their exhibits a red shift as the silicon chain becomes longer. The UV spectra of some polysilanes were found to be thermochromic." This is due to conformational changes in the backbone. Conformational dependence of... 

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