Network polysilanes

Network Polysilanes, Polysilane Dendrimers, and Ladder Polysilanes... 

In recent years polysilane dendrimers have been synthesized in several laboratories. Two examples are shown in schemes 5.7128 and 5.8.129 The dendrimers have electronic absorption spectra similar to those of the longest silicon chains present, but with intensity about ten times as great. Like the network polysilanes, these dendrimers display weak visible emission spectra, perhaps resulting from localized excitations at the branching points. The field of polysilane dendrimers in the subject of a recent authoritative review.130... 

Completely networked polysilanes show a variation of n and k with the degree of cross-linking compared to parent linear polysilanes. 

C-O bond cleavage is most efficiently set up in strained systems, e.g. in oxiranes [26] and oxetanes [27], whereas 0-0 bond cleavage in cyclic peroxides [28] and C-S [29] and C-Se [30] bond rupture occur efficiently even in unstrained compounds. Si(Ge)-Hal bond cleavage [31] has become a valuable reaction, e.g. in the preparation of network polysilanes and polygermanes [32]. 

In addition to polysilanes we will also briefly look at some other polymer systems that contain silicon. These are known as polysilynes or network polysilanes, polycarbosilanes, and polysiloles. 

Okano M, Nak ura K, Yamada K, Hosoda N, Wakasa M (2006) An improvement electrochemical synthesis of network polysilanes. Electrochemistry 74(12) 956-958... 

The experimental observations of red shifts of the UV absorptions tails with increase in silicon dimensionality were corroborated by ZINDO-calculated spectra comparing linear polysilane, network polysilyne, crystalline cluster, and amorphous cluster structures, which showed respectively lowest absorption transition energies of 5.38 eV (230.4 nm), 4.60eV (269.5nm), 4.57eV (271.2nm), and 2.46eV (503.9nm), as shown in Figure 57.362... 

Demoustier-Champagne, S. Devaux, J. Polysilanes and copolymers synthesis and characterization. In Recent Research Developments in Polymer Science-, Pandalai, S. G., Ed. Transworld Research Network Trivandrum, 1998 Vol. 2, pp 1—27. 

Polymer or polymer network with a skeletal strueture that does not inelude carbon atoms. Note Examples include polyphosphazenes, polysilieates, polysiloxanes, polysilanes, polysilazanes, polygermanes, polysulfides, ete. 

Much of the interest in the polysilanes, polygermanes, and polystannanes involves their sigma delocalization and their sigma-pi delocalization when coupled with arenes or acetylenes. This is not unexpected since silicon exists as a covalent network similar to diamond. In exhibiting electrical conductivity, germanium and tin show more typical metallic bonding. Some polystannanes have been referred to as molecular metals. ... 

Siloxanes Polyphosphazenes Polyphosphate esters Polysilanes Sol-gel networks... 

Most linear polysilanes show bright resonant luminescence in the UV region but network and branched polysilanes show luminescence in the visible... 

Band gap dependence on network dimensions and unit numbers is summarized in Figure 5. Curve u shows the variation irom disilane to polysilane. For curve v, n = 1 corresponds to polysilane, and n = 2 corresponds to a ladder polymer the limiting case is siloxene. Curve w shows the energy gap changes for superlattices of different layer thickness, and it approaches the curve for crystalline silicon. 

Silicon-based polymers form a dimensional hierarchy from disilanes, to crystal silicon, and through polysilanes, ladder polymers, siloxenes, polysilane alloys, clusters, and amorphous silicons and include unsaturated systems, such as polysilenes, hexasilabenzenes, and so on. Their properties depend basically on the network dimensions and can vary from conducting (metallic) and semiconducting to insulating. 

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