The order–disorder conundrum: a trade-off between crystalline and amorphous porous organic polymers for task-specific applications

Abstract

Porous organic polymers (POPs) have received increasing attention due to their properties, such as permanent porosity with tunable pore size, robust structure, high surface area, and versatility of the backbone for the desired function. Such properties prove to be quite valuable for a plethora of sustainable applications. POPs can largely be classified as crystalline or amorphous based on the degree of long-range order. Crystalline POPs such as two-dimensional covalent organic frameworks possess characteristics such as unimodal pores with long one-dimensional pore channels allowing size-selective guest recognition, whereas amorphous network POPs give rise to a hierarchical pore size distribution enabling facile ion and mass transport. Since structure plays an undeniably vital role in the function, POPs with contrasting degrees of long-range order are suitable for some applications more than others. To address this conundrum, here we discuss at length the impact of the extent of structural order of the POPs in the context of four key applications, namely water treatment, electrochemical energy storage, heterogeneous catalysis, and optical sensing along with light-harvesting. Additionally, the formation principles of POPs with varying degrees of long-range order in view of kinetics and thermodynamics have been outlined. Furthermore, we provide a general guideline for the specific use of crystalline and amorphous POPs along with future avenues of exploration mitigating the current challenges towards the design of task-specific new-generation functional porous materials.