Hybrid organic-inorganic sol-gel materials containing silica were first called “ORMOSILs” in 1984.1 Since then, the number of hybrid organicinorganic combinations has increased rapidly.2 Hybrid materials have remarkable features resulting from the synergistic combination of both inorganic and organic components that make them suitable for a wide range of applications such as electrochemical devices, biomedical applications including drug delivery, and electronic and optoelectronic applications including light-emitting diodes, photodiodes, solar cells, gas sensors and field effect transistors.
Generally, organic-inorganic materials are classified in two broad categories: Class I materials where the organic and inorganic components are embedded one within the other and display weak bonds, and Class II materials where there are strong covalent bonds between the inorganic and organic components.3
For more than 25 years hybrid gels have been grown by sol-gel process.4 Since sol-gel processing is a low temperature method, it is only natural that sol-gel processing has been extended to hybrid materials with retained organic content. Ordinarily, the outcome of the sol-gel process with the precursor tetraethylorthosilicate (TEOS) (Aldrich Prod. No. 333859) is a 3-dimensional network. TEOS, with 4 identical groups attached to Si, undergoes hydrolysis and polycondensation reactions. The 4 identical groups can be changed to, for example, 3 identical groups and one group with a direct Si-C bond. While the remaining 3 ethoxy groups are reactive to hydrolysis, the substituted group, for example, methyl, is not.