An intramolecular formal [3+2] cycloaddition of activated aziridines and epoxides with electron-deficient alkene has been developed for the general and efficient construction of bridged aza-and oxa-[n.2.1] (n = 3 or 4) skeletons. This strategy can be efficiently promoted by lithium iodide. To demonstrate its potential, the intramolecular formal [3+2] cycloaddition was used to access the important intermediate of homoepiboxidine.

In this work, three organic–inorganic hybrid calixpyridinium–polyoxometalate nanoparticle assemblies were constructed by the strong electrostatic interactions of calixpyridinium with phosphotungstic acid (PTA, H3PW12O40), silicotungstic acid (STA, H4SiW12O40), and phosphomolybdic acid (PMA, H3PMo12O40). Interestingly, the three assemblies were all irregular, spherical nanoparticles but with quite different sizes. The smallest calixpyridinium–PTA nanoparticle assembly had the most excellent removal effect on organic dyes, such as crystal violet (CV), eriochrome black T (EBT), and congo red (CR) in the presence of H2O2 and light. This effect became worse and worse when using a larger and larger nanoparticle assembly from calixpyridinium–STA to calixpyridinium–PMA under the same conditions. In addition, the solid phosphoric calixpyridinium–PTA and calixpyridinium–PMA assemblies had a selective adsorption capacity for cationic organic dyes, such as CV, methylene blue (MB), and rhodamine B (RhB), under acidic conditions. This study not only gave a structure–function relationship of calixpyridinium–polyoxometalate organic–inorganic hybrid nanoparticle assemblies but also supplied an alternative green and convenient method for the removal of organic dyes from wastewater.

A pH-triggered transition from micellar aggregation to a host−guest complex was achieved based on the supramolecular interactions between calixpyridinium and pyrroloquinoline quinone disodium salt (PQQ-2Na) accompanied by a color change. Our design has the following three advantages: (1) a regular spherical micellar assembly is fabricated by the supramolecular interactions between calixpyridinium and PQQ-2Na at pH 6 in an aqueous solution, (2) increasing the pH can lead to a transition from micellar aggregation to a host−guest complex due to the deprotonation of calixpyridinium, and at the same time (3) increasing the pH can lead to a color change owing to the deprotonation of calixpyridinium and the complexation of deprotonated calixpyridinium with PQQ-2Na. Benefitting from the low toxicity of calixpyridinium and PQQ-2Na, this pH-induced transition from micellar aggregation to a host−guest complex was further studied as a controllable-release model.

In this work, a spherical calixpyridinium-IR-820 supramolecular assembled material was fabricated based on the calixpyridiniuminduced IR-820 aggregation. This assembled material exhibited a well visible light responsiveness by the photodecomposition of aggregated IR-820 accompanied by an obvious color change. Such photochromic material has many potential applications. More interestingly, the photodecomposition of aggregated IR-820 was significantly promoted, although the aggregated photosensitizers usually exhibited a lower photoreactivity. This approach can be further extended to construct various visible-light responsive supramolecular assembled materials and potentially applied in many fields. Herein, benefitting from the pH-dependent luminescent properties of calixpyridinium and the photodegradation products of IR-820, a pH-controlled visual multicolor luminescence was achieved, which was perfectly applied in the detection of pH from 5 to 10 by naked eyes.

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