An indole-based microporous organic polymer (PINK) has been obtained by the condensation polymerization of 1,3,5-tris-(4-fluorobenzoyl)benzene with 3,3′-diindolylmethane via a catalyst-free nucleophilic substitution reaction. Due to the local dipole–π interactions between indole and carbon dioxide (CO₂), the uptake capacity for CO₂ reaches up to 16.0 wt% (1.0 bar, 273 K), and the high (CO₂/N₂ = 15, CO₂/CH₄ = 32) selectivities of the polymer make it a promising material for potential application in gas separation. Furthermore, the hydrogen storage is up to 2.48 wt% (1.0 bar, 77 K). In comparison to the reported porous organic polymers, the preparative strategy exhibits cost-effective advantages, which are essential for scale-up preparation. Its good performance for H₂ storage and CO₂ separation suggests that PINK with a large specific surface area shows potential use in clean energy applications and the environmental field.

A novel indole-based aerogel (4-HIFA) has been obtained by the condensation of 4-hydroxyindole and formaldehyde via sol–gel technology, which proceeds easily by acid catalysis in one pot. Taking advantage of the synergistic effects of the complexation and cation–π interactions of the hydroxyl and indole groups with heavy metals, the 4-HIFA exhibits enormous capacities for Ni²⁺ (∼240 mg g⁻¹), Cu²⁺ (∼265 mg g⁻¹), Cr³⁺ (∼92 mg g⁻¹) and Zn²⁺ (∼125 mg g⁻¹), a selectivity order of Ni²⁺ > Cu²⁺ > Cr³⁺ > Zn²⁺, and a very high distribution coefficient (K_d) of ∼10⁵ mL g⁻¹ which place it at the top of materials known for such removal. Furthermore, the adsorptions for all of the four ions reach equilibrium within ∼5 min. As an efficient, low-cost and renewable adsorbent, 4-HIFA is thus promising for use in the processing of large amounts of sewage.

Force-reversible C-N bonds, resulting from the click chemistry reaction between triazolinedione (TAD) and indole derivatives, offer exciting opportunities for molecular-level engineering to design materials that respond to mechanical loads. Here, we displayed that TAD-indole adducts, acting as crosslink points in dry-state covalently crosslinked polymers, enable materials to display reversible stress-responsiveness in real time already at ambient temperature. Whereas the exergonic TAD-indole reaction results in the formation of bench-stable adducts, they were shown to dissociate at ambient temperature when embedded in a polymer network and subjected to a stretching force to recover the original products. Moreover, the nascent TAD moiety can spontaneously and immediately be recombined after dissociation with an indole reaction partners at ambient temperature, thus allowing for the adjustment of the polymer segment conformation and the maintenance of the network integrity by force-reversible behaviors. Overall, our strategy represents a general method to create toughened covalently crosslinked polymer materials with simultaneous enhancement of mechanical strength and ductility, which is quite challenging to achieve by conventional chemical methods.

We have successfully synthesized a novel type of recyclable indole-based porous polymer, which possesses highly effective capture behavior for iodine in aqueous solution via the synergistic effects of cation–π and electrostatic forces. More interestingly, the absorption performance can be efficiently detected via a visual colorimetric assay using a smartphone.