Reticulating Node-Linker-Modulator Chemical Spaces for Modular Design of Glasses and Liquids

Network-forming glasses linked up by molecular building blocks through strong bonds are emerging new materials that can combine the processability of glasses and modular designability of reticular frameworks. The key challenge to achieve modular designability and structural diversity for molecular network-forming glasses arise from their strong and directional linkages between molecular building blocks restricting configurational motion needed for vitrification and liquification. Herein, we show that introducing network modulators can facilitate configurational motion by dynamic exchange and reduction of network connectivity, which represent a highly generic strategy to facilitate the vitrification of networks linked with strong bonds. Consequently, node-linker-modulator represent a generic formula for synthesizing molecular network-forming glasses, which can be applied both for metal-organic networks and covalent organic networks. The modular designability of the node-linker-modulator chemical spaces is demonstrated with titanium, zirconium and boron-based nodes, various multi-dentate alcohol linkers and monodentate alcohol modulators. Systematically tuning the modulator ratio gives universal scaling of viscosity and heat capacity jump associated with glass transition, which clearly shows how modulator would increase glass forming ability. The modular designability is exploited for rationally synthesizing fluorescent molecular network-forming glasses with high quantum yield, which can be integrated into electroluminescent devices. The current development represents an important expansion of reticular chemistry into the regime of glassy materials.