Design of a Unique Energy-Band Structure and Morphology in a Carbon Nitride Photocatalyst for Improved Charge Separation and Hydrogen Production

We report the facile and environmental-friendly synthesis of an efficient carbon nitride photocatalyst for hydrogen production and dyes degradation by using a unique supramolecular assembly with an element gradient as the reactant. The element gradient is acquired through the selective removal of barbituric acid from the surface of a supramolecular assembly that comprises barbituric acid, melamine, and cyanucric acid, using hydrochloric acid as a surface modifier. The tailored design of the supramolecular aggregate results in inner and outer parts, which have carbon-rich and carbon-poor domains, respectively. Structural and optical investigations of the new assemblies reveal that the hydrogen–chlorine interaction generates a carbon gradient through the starting supramolecular assembly and to a better packing and structural alignment of the supramolecular units. Detailed X-ray photoelectron spectroscopy and photophysical studies of the final carbon nitride-like materials after calcination at 550 °C indicate that the element gradient across the starting precursor directly projects on the final carbon nitride chemical and element composition, as well as on its optical and photocatalytic properties. The spatial arrangement of the starting monomers leads to the formation of a unique energy-level structure in the final material, which is intended to improve the efficiency of charge separation under illumination and, thereby, result in a strong enhancement of photocatalytic activity toward a high hydrogen production and fast dyes degradation. This work provides new opportunities for the rational design of carbon nitride and other metal-free materials with unique and controllable chemical, optical, and catalytic properties for sustainable energy-related applications

Photocontrol over Cucurbit[8]uril Complexes: Stoichiometry and Supramolecular Polymers

Herein we report the photocontrol of cucurbit[8]­uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host–guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of <i>Z</i>-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state

Photocontrol over Cucurbit[8]uril Complexes: Stoichiometry and Supramolecular Polymers

Herein we report the photocontrol of cucurbit[8]­uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host–guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of <i>Z</i>-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state

Photocontrol over Cucurbit[8]uril Complexes: Stoichiometry and Supramolecular Polymers

Herein we report the photocontrol of cucurbit[8]­uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host–guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of <i>Z</i>-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state

Photocontrol over Cucurbit[8]uril Complexes: Stoichiometry and Supramolecular Polymers

Herein we report the photocontrol of cucurbit[8]­uril (CB[8])-mediated supramolecular polymerization of azobenzene-containing monomers. The CB[8] polymers were characterized both in solution and in the solid state. These host–guest complexes can be reversibly switched between highly thermostable photostationary states. Moreover, a remarkable stabilization of <i>Z</i>-azobenzene was achieved by CB[8] complexation, allowing for structural characterization in the solid state

The Importance of Excess Poly(<i>N</i>‑isopropylacrylamide) for the Aggregation of Poly(<i>N</i>‑isopropylacrylamide)-Coated Gold Nanoparticles

Thermoresponsive materials are generating significant interest on account of the sharp and tunable temperature deswelling transition of the polymer chain. Such materials have shown promise in drug delivery devices, sensing systems, and self-assembly. Incorporation of nanoparticles (NPs), typically through covalent attachment of the polymer chains to the NP surface, can add additional functionality and tunability to such hybrid materials. The versatility of these thermoresponsive polymer/nanoparticle materials has been shown previously; however, significant and important differences exist in the published literature between virtually identical materials. Here we use poly­(<i>N</i>-isopropylacrylamide) (PNIPAm)-AuNPs as a model system to understand the aggregation behavior of thermoresponsive polymer-coated nanoparticles in pure water, made by either grafting-to or grafting-from methods. We show that, contrary to popular belief, the aggregation of PNIPAm-coated AuNPs, and likely other such materials, relies on the size and concentration of unbound “free” PNIPAm in solution. It is this unbound polymer that also leads to an increase in solution turbidity, a characteristic that is typically used to prove nanoparticle aggregation. The size of PNIPAm used to coat the AuNPs, as well as the concentration of the resultant polymer–AuNP composites, is shown to have little effect on aggregation. Without free PNIPAm, contraction of the polymer corona in response to increasing temperature is observed, instead of nanoparticle aggregation, and is accompanied by no change in solution turbidity or color. We develop an alternative method for removing all traces of excess free polymer and develop an approach for analyzing the aggregation behavior of such materials, which truly allows for heat-triggered aggregation to be studied

Self-Assembly and Photoinduced Optical Anisotropy in Dendronized Supramolecular Azopolymers

Herein we report the preparation and characterization of dendronized supramolecular polymers composed of a carboxy-terminated azodendron, dAZO, and two different vinylpyridine-containing polymers: poly­(4-vinylpyridine) (P4VP) and polystyrene<i>-<i>b</i>-</i>poly­(4-vinylpyridine) (PS<i>-<i>b</i>-</i>P4VP) block copolymer. P4VP can selectively complex dAZO through hydrogen-bonding interactions, thus resulting in liquid crystalline materials. Additionally, this strategy is also applicable to the preparation of dendronized supramolecular block copolymers (BCs). Lamellar, cylindrical, and spherical morphologies are observed for the BC complexes depending on the dAZO to vinylpyridine repeating unit ratio. Photoinduced orientation of the azobenzene moieties is obtained in films of the H-bonded materialsboth P4VP and PS<i>-<i>b</i>-</i>P4VP based complexesby using 488 nm linearly polarized light and characterized through birefringence and dichroism measurements. High and stable values of birefringence are obtained for polymers with azobenzene content as low as 2.7 wt %, thus demonstrating the benefits of preorganization in photoactive dendritic moieties in side-chain H-bonded materials

Triply Triggered Doxorubicin Release From Supramolecular Nanocontainers

The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]­uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly­(<i>N</i>-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly­(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers

Efficient Host–Guest Energy Transfer in Polycationic Cyclophane–Perylene Diimide Complexes in Water

We report the self-assembly of a series of highly charged supramolecular complexes in aqueous media composed of cyclobis­(4,4′-(1,4-phenylene)­bispyridine-<i>p</i>-phenylene)­tetrakis­(chloride) (ExBox) and three dicationic perylene diimides (PDIs). Efficient energy transfer (ET) is observed between the host and guests. Additionally, we show that our hexacationic complexes are capable of further complexation with neutral cucurbit[7]­uril (CB[7]), producing a 3-polypseudorotaxane via the self-assembly of orthogonal recognition moieties. ExBox serves as the central ring, complexing to the PDI core, while two CB[7]­s behave as supramolecular stoppers, binding to the two outer quaternary ammonium motifs. The formation of the 3-polypseudorotaxane results in far superior photophysical properties of the central PDI unit relative to the binary complexes at stoichiometric ratios. Lastly, we also demonstrate the ability of our binary complexes to act as a highly selective chemosensing ensemble for the neurotransmitter melatonin