Reversible structural transformation of supramolecular inorganic–organic hybrid glasses and zeolitic-imidazolate frameworks

Abstract

Zeolitic-imidazolate frameworks (ZIFs) are porous coordination polymer networks which can be vitrified to bulk glasses using a conventional melt-quenching technique. Here, we report the vitrification of a two-dimensional (2D) ZIF-7-III network to a highly transparent supramolecular glass via a network-solvation approach, in which the ZIF network is interrupted by ethanol/HNO₃ solution. Surprisingly, the as-synthesized glass could reversibly crystallize to 2D ZIF-7-III crystals using a dissolution–recrystallization method. The reversible structural transformation, composition, thermodynamics, and optical properties of the as-synthesized ZIF-7-III crystals and supramolecular glasses containing mixed linkers were investigated. By controlling the glass composition, the network flexibility was adjusted to increase the alignment of luminescent dye molecules during the mechanical fiber drawing process and thus polarized luminescence with a large polarization ratio (∼56%) was detected from the dye doped fibers. These results improve our understanding of the crystallization/vitrification process of inorganic–organic hybrid materials, which may enable the discovery of novel hybrid glasses with various functionalities.