Molecular sieves are very effective matrices for hosting chromophore molecules and for arraying them within their uniform, well ordered pores. Some of chromophores are very unstable and easily decompose under contact with oxygen, water or other reagents as well as under exposition to light or elevated temperature. The entrapped molecules always gain much higher stability. Their photophysical properties are much different to those of pristine chromophores. The guest molecules can be encapsulated inside the voids or they can be introduced by simple adsorption and then stabilized by blocking the pores. The guest molecules can also be stabilized by means of chemical bonds with the framework, with host cations or functional groups (sometimes grafted on the inner surface). Some molecules can be introduced inside molecular sieves upon their crystallization. It seems that the guest molecules may be efficiently entrapped in the metal organic framework (MOF) materials.
Some natural zeolites (lazurite, sodalite) show intense colouration and can be applied as pigments. The sulphur radicals responsible for the deep ultramarine colour can be generated inside the zeolite cages (mostly β-cages) and ultramarine analogues (with various hues) can be prepared under much milder conditions than those applied in the conventional process. Other sulphur chromophores (thiocarbonates, 1,3-dithiole-2-thione-4,5-dithiolato (dmit)) can be introduced into zeolites. Zeolites and other molecular sieves can host indigo and its derivatives to form Maya Blue analogues of various hues depending on the nature of the cations introduced into zeolite matrices. Many other organic and inorganic (e.g. CdS) coloured compounds can be introduced into the molecular pore systems and form colorants, luminophores, sensors, optical and microelectronic devices or even lasers. The role of pigment matrices can be also taken by pillared clays and some porous silicas.
Keywords: Dyes, Entrapment, Encapsulation, Guest molecule organization, Indigo, Luminescence, Maya Blue, Molecular sieves, Pigments, Resistibility, Stability, Ultramarine, Zeolites
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