Systematic extension of the length of the organic conjugated pi-system of mesoporous silica-based organic-inorganic hybrid materials

The first systematic investigations on the optical properties of mesoporous silica-based organic inorganic hybrid materials is reported. It could be shown that the optical absorption properties of the incorporated organic functionalities are tuneable by adjusting the length of the conjugation of the pi-electron systems or by integration of heteroatoms therein. For this purpose, two new bis-silylated compounds with 18 pi-electron systems, namely 4,4'-bis((E)-2-(triethoxysilyl)vinyl) stilbene and 1,2-bis(4-((E)-2-(triethoxysilyl) vinyl) phenyl) diazene and their related mesoporous hybrid materials, were synthesised. On the basis of solid state UV-vis absorption spectra it is demonstrated that for highly conjugated and elongated organic bridges the absorption maximum reaches the visible region resulting in a yellow powder for a pure hydrocarbon backbone and a deep red powder for an azobenzene containing material.