Functional Scaffolds from AIE Building Blocks

Abstract

Summary In materials science, the whole is typically greater than the sum of the parts. This principle has been spotlighted in advanced molecular materials, where the assembly of fundamental building blocks at the molecular scale can lead to a hierarchy of materials with enhanced properties, sometimes with new functions at larger scales. One exciting example is the phenomenon of aggregation-induced emission (AIE). In contrast to a single free molecule that exhibits no or weak luminescence, aggregation of AIE fluorogens can produce a plethora of solid-state luminescent materials. In this Review, we explore the synergistically collective behaviors of multiple AIE units in ordered arrays by investigating scaffolding materials ranging from discrete cage compounds to infinite crystalline frameworks. As shown, AIE building blocks endow the materials with intriguing luminescence properties: intensive and tunable emission, unprecedented activities in specific emission modes (such as room temperature phosphorescence, multiphoton-excitable luminescence, coherent harmonic generation, circularly polarized luminescence, and lasing), stimulus-responsive luminescence for chemosensing and bioimaging, etc. In contrast, conventional building blocks frequently suffer from faint or extinguished emission in these scaffolding materials. Furthermore, the self-reporting luminescence properties endowed by built-in AIE building blocks were integrated into essential functions such as matter adsorption and diffusion, light harvesting, and photocatalysis. In addition to their unique configurations, processability, and facile derivatization chemistries, AIE-active building blocks in scaffolds act as the origin of a new phase of matter. This work helps to motivate the exploration of "advisable aggregation effects" in emerging functions of material systems.