Porous organic polymers (POPs) are organic macromolecules that are considered emerging materials because of their high specific surface areas, tunable porosities, low densities, high chemical and thermal stabilities, variable compositions, convenient post-functionalization, extended π-conjugations, and their high contents of carbon, nitrogen, oxygen, and other non-metallic atoms. POPs have been classified into four types: covalent triazine frameworks (CTFs), hypercrosslinked polymers (HCPs), covalent organic frameworks (COFs), and conjugated microporous polymers (CMPs). These materials have potential applications in, for example, gas capture/separation, energy storage, H₂ production from water, photocatalysis, chemical sensing, perovskite solar cells, water treatment, optical devices, and biomedicine. In this review, we provide an overview of recent reports describing the preparation and various applications of POPs.

Importance of monomer symmetry, planarity, and nitrogen content in the crystallinity, surface area, and CO ₂ uptake has been studied for two series of 2D-COFs.

In this paper we report the extremely crystalline structures, high thermal stabilities, and strong fluorescence emissions of covalent organic frameworks (COFs) based on linked carbazole units. We have synthesized three stable luminescent carbazole-linked COFs, namely, BCTB–PD, BCTA–TP, and BCTB–BCTA, through Schiff base condensations of 4,4′,4′′,4′′′-([9,9′-bicarbazole]-3,3′,6,6′-tetrayl)tetrabenzaldehyde (BCTB-4CHO) with p-phenylenediamine (PD), of 4,4′,4′′,4′′′-([9,9′-bicarbazole]-3,3′,6,6′-tetrayl)tetraaniline (BCTA-4NH₂) with terephthalaldehyde (TP), and of BCTB-4CHO with BCTA-4NH₂, respectively. These COFs had large Brunauer–Emmett–Teller surface areas (up to 2212 m² g⁻¹) and outstanding thermal stabilities (decomposition temperatures of up to 566 °C). Interestingly, the intramolecular charge transfer (ICT) and fluorescence properties of these COFs were strongly influenced by their types of Schiff base bonding (BCTB-4CHN or BCTA-4NCH) and the degrees of π-stacking between their COF layers. For example, ICT from the electron-donating carbazole group to the acceptor through the Schiff base units of the type BCTB-4CHN and increasing the π-stacking distance enhanced the fluorescence emission from the COF. Moreover, BCTB–BCTA, the most fluorescent of our three COFs, functioned as a fluorescent chemosensor for HCl in solution, with outstanding sensitivity and a rapid response.

In this work, two-dimensional conjugated covalent organic frameworks (2D-COF) based on a building block of tetraphenylethylene are successfully developed. Bicarbazole and pyrene moieties are respectively coupled with 4,4′,4′′,4′′′-(ethane-1,1,2,2-tetrayl)tetranilino (ETTA) via [4 + 4] solvothermal condensation conditions of 3,3′,6,6′-tetraformyl-9,9′-bicarbazole (Car-4CHO) and 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) to afford Car-ETTA and TFPPy-ETTA COFs. According to thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and N₂ adsorption and desorption measurements, both Car-ETTA and TFPPy-ETTA COFs exhibit excellent thermal stability, highly crystalline structure, and high specific surface area, respectively. These findings are supported by force field and ab initio calculations. Furthermore, successful applications of these COFs in perovskite solar cells (PVSCs) are demonstrated owing to their well-conjugated properties and π–π interactions. While serving as interlayers in the devices, these COFs could effectively promote the interfacial charge dynamic to further optimize the resulting performance. Besides, certain interaction between COFs and perovskite also leads to an improved morphology and crystallinity of the perovskite layer, presenting defect passivation capability. As a result, we show that the performance of the COF-modified PVSC could be improved from 17.40 to 19.80%.