Modification of Molecular Sieves and Silica Surfaces Aiming the Immobilization of Chromophores - Synthesis of Photochromic Nanocomposite Materials

Synthesis and characterization of photochromic host-guest materials are main goals of the present work. Strong interactions of chromophores with the inorganic support yield in diffusion stability and exceptional optical properties, specifically changed by modification of the host lattice. Apart from photochromic dyes (azo, diarylethene, spiropyran, spirooxazine) other functional chromophores were applied for preparation of nanocomposites.:p:Microporous aluminosilicate faujasite (zeolite Y), mesoporous Si-MCM-41 and thin films were used as hosts. The supercage of the 3-D system of zeolite Y has a dimension of 1.3 nm and is accessible by smaller pores. Thus, in-situ reaction of educts leads to encapsulation of spiropyrans. The class of ordered mesoporous materials opened the way for incorporation of sterically demanding guests. Si MCM 41 was obtained by homogenous precipitation (pore size 3.2 nm) and was modified in a multi-step procedure. Blocking of outer surface with diphenyldichlorosilane ensured the exclusive functionalization of the inner surface with various alkoxysilanes. Finally, the dyes were grafted either covalently (peptide, sulfonamide and anhydride imide bonds) or ionically.:p:Solid state methods (sorption measurement, XRD, DRIFT, r-UV/VIS, SEM and TEM) were used for monitoring the modification of the porous materials, e.g. regioselectivity of outer surface passivation of Si MCM 41. Confocal fluorescence microscopy designated homogeneous distribution even at lowest dye concentrations.:p:The crucial advantage of modified Si MCM 41 is the interaction of photoisomers with the chemical environment. Thermal relaxation after reverse photochromism of photomerocyanine forms of anchored spirochromes was delayed or stopped. The cage effect of the void structure of zeolite Y was demonstrated by the stability of the transoid spyropyran isomers. The reverse-photochromic behavior could also be controlled by the Si/Al-ratio