TY - JOUR AB - The reversible photoisomerization of azobenzene has been utilized to construct a plethora of systems in which optical, electronic, catalytic, and other properties can be controlled by light. However, owing to azobenzene’s hydrophobic nature, most of these examples have been realized only in organic solvents, and systems operating in water are relatively scarce. Here, we show that by coadsorbing the inherently hydrophobic azobenzenes with water-solubilizing ligands on the same nanoparticulate platforms, it is possible to render them essentially water-soluble. To this end, we developed a modified nanoparticle functionalization procedure allowing us to precisely fine-tune the amount of azobenzene on the functionalized nanoparticles. Molecular dynamics simulations helped us to identify two distinct supramolecular architectures (depending on the length of the background ligand) on these nanoparticles, which can explain their excellent aqueous solubilities. Azobenzenes adsorbed on these water-soluble nanoparticles exhibit highly reversible photoisomerization upon exposure to UV and visible light. Importantly, the mixed-monolayer approach allowed us to systematically investigate how the background ligand affects the switching properties of azobenzene. We found that the nature of the background ligand has a profound effect on the kinetics of azobenzene switching. For example, a hydroxy-terminated background ligand is capable of accelerating the back-isomerization reaction by more than 6000-fold. These results pave the way toward the development of novel light-responsive nanomaterials operating in aqueous media and, in the long run, in biological environments. AU - Chu, Zonglin AU - Han, Yanxiao AU - Bian, Tong AU - De, Soumen AU - Král, Petr AU - Klajn, Rafal ID - 13373 IS - 5 JF - Journal of the American Chemical Society KW - Colloid and Surface Chemistry KW - Biochemistry KW - General Chemistry KW - Catalysis SN - 0002-7863 TI - Supramolecular control of azobenzene switching on nanoparticles VL - 141 ER - TY - JOUR AB - The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chemical networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochemistry brings conceptually new demonstrations. Especially attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chemistry and nanoparticle core composition in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chemical stimuli such as solvent, pH, gases, metal ions or biomolecules. It then focuses on physical stimuli: temperature, magnetic and electric fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges. AU - Grzelczak, Marek AU - Liz-Marzán, Luis M. AU - Klajn, Rafal ID - 13372 IS - 5 JF - Chemical Society Reviews KW - General Chemistry SN - 0306-0012 TI - Stimuli-responsive self-assembly of nanoparticles VL - 48 ER - TY - JOUR AB - Arylazopyrazoles represent a new family of molecular photoswitches characterized by a near-quantitative conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd–imidazole coordination. Owing to its high water solubility, the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not soluble in water. NMR spectroscopy and X-ray crystallography have independently demonstrated that each cage can encapsulate two molecules of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calculations suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage. AU - Hanopolskyi, Anton I AU - De, Soumen AU - Białek, Michał J AU - Diskin-Posner, Yael AU - Avram, Liat AU - Feller, Moran AU - Klajn, Rafal ID - 13369 JF - Beilstein Journal of Organic Chemistry KW - Organic Chemistry TI - Reversible switching of arylazopyrazole within a metal–organic cage VL - 15 ER - TY - JOUR AB - Efficient isomerization of photochromic molecules often requires conformational freedom and is typically not available under solvent-free conditions. Here, we report a general methodology allowing for reversible switching of such molecules on the surfaces of solid materials. Our method is based on dispersing photochromic compounds within polysilsesquioxane nanowire networks (PNNs), which can be fabricated as transparent, highly porous, micrometer-thick layers on various substrates. We found that azobenzene switching within the PNNs proceeded unusually fast compared with the same molecules in liquid solvents. Efficient isomerization of another photochromic system, spiropyran, from a colorless to a colored form was used to create reversible images in PNN-coated glass. The coloration reaction could be induced with sunlight and is of interest for developing “smart” windows. AU - Chu, Zonglin AU - Klajn, Rafal ID - 13370 IS - 10 JF - Nano Letters KW - Mechanical Engineering KW - Condensed Matter Physics KW - General Materials Science KW - General Chemistry KW - Bioengineering SN - 1530-6984 TI - Polysilsesquioxane nanowire networks as an “Artificial Solvent” for reversible operation of photochromic molecules VL - 19 ER - TY - JOUR AB - Diamondoid nanoporous crystals represent a synthetically challenging class of materials that typically have been obtained from tetrahedral building blocks. In this issue of Chem, Stoddart and coworkers demonstrate that it is possible to generate diamondoid frameworks from a hexacationic building block lacking a tetrahedral symmetry. These results highlight the great potential of self-assembly for rapidly transforming small molecules into structurally complex functional materials. AU - Białek, Michał J. AU - Klajn, Rafal ID - 13371 IS - 9 JF - Chem KW - Materials Chemistry KW - Biochemistry (medical) KW - General Chemical Engineering KW - Environmental Chemistry KW - Biochemistry KW - General Chemistry SN - 2451-9308 TI - Diamond grows up VL - 5 ER -