Siloxene-like polymer

TABLE 2. Fluorescence maxima and appearance of siloxene-like polymers derived from compounds 1-12... 

New Results in Cyclosilane Chemistry Siloxene-like Polymers... 

Siloxene-like Polymers from Molecular Precursors... 

One of the basic properties of siloxenes is their general insolubility in organic solvents, a fact that strongly impedes physical and structural characterization. As a result, the question arose as to whether structurally better defined siloxene-like polymers with improved solubility can be assembled in a stepwise manner starting from appropriate molecular precursors, and whether the properties of siloxene, such as the intense photoluminescence, can be matched. We thus attempted to rebuild the proposed structure of Kautsky-siloxene by the controlled hydrolysis of cyclic or linear oligosilanes bearing hydrolytically labile substituents followed by the thermal condensation to polymeric siloxanes. The general route is outlined in Scheme 16.1. 

Figure 16.2. Normalized fluorescence spectra of selected siloxene-like polymers (the molecular precursors used for polymer preparation are indicated above the spectra).

Summary In continuation of our previous contributions concerning the fluorescence behavior of polysiloxanes containing oligosilanyl substructures, the photoluminescence of hydrolysis and condensation products derived from di- and trifiinctional cyclooligosilanes has been investigated. To our present knowledge there are two conditions to be met for our siloxene-like polymers in order to exhibit fluorescence the presence of cyclosilanyl subunits and a two- or three-dimensional polymeric structure. 

Since only polymers obtained from the cyclic starting materials 5, 6, 7, 10, 11 and 12, which are likely to have siloxene-like structures, exhibit color and fluorescence, the polysilane ring seems to be essential for the exceptional optical properties of siloxene. This is in agreement with the original idea of Kautsky, who assumed the cycle to be the chromophore. 

To elucidate the question whether or not cyclosilane structures are essential for the color and fluorescence of the polymers, linear and cyclic silanes with silicon halogen or -triflate functions were prepared and hydrolyzed to siloxene-like structures. 

Scheme 16.1. General reaction scheme for the synthesis of polymers with siloxene-like structures.

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

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