We work on finding possible chemical reactions which can be driven by macroscopically non-damaging mechanical compression of flexible polymers. Starting with the homolytical cleavage upon mechanical treatment, polymer surfaces develop radicals which may initiate many reactions such as metal nanoparticle synthesis or polymerization. The process is environment-friendly and recyclable; the polymers may be used without significant loss of efficiency for many cycles.

We study the self-assembly of oppositely charged nanoparticles on the surfaces of microcrystals (mCs) comprised of various inorganic salts during their growth. We found out that oppositely charged NPs can act as “surfactants” to control the growth of such microcrystals. The formation of NP-coated mCs results from subtle interplay between crystal growth and the cooperative adsorption of NPs onto the growing crystals. These NP coatings can act as protective layers and limit solubility of the crystals or even render them completely insoluble.

Self-assembly of oppositely charged NPs mediated by copper sulfate salt leads to novel composite (NP-salt) assemblies is characterized by new morphology, distinct from NP-NP self-assembled “diamonds” or NP-coated inorganic crystals. We investigate the mechanism and scope of this shape- and size-directed NP self-assembly.

In this project, we investigate the icosahedral and spherical nanoparticles grafted with charge end group ligands in solutions. Different conformations of grafted ligands are observed. We found that for certain ratio of electostatic repulsion between the end groups over Van der Waals attraction between ligands, ridges are formed on the nanoparticle surface.

Mounting molecular switches that are little more than one cubic nanometer in size as pendants dangling from polymer chains could have profound implications for the development of nanoelectronics based on a bottom-up approach to device fabrication. To this particular end, a high molecular weight polymer with pendant [2]catenanes — a molecular entity composed of two mechanically interlocked rings which can undergo relative movements of a “quantized” nature with respect to each other — has been designed and produced in the laboratory under thermodynamic control using a procedure that is reminiscent of the conjurer’s trick where two metal rings become interlocked together as if by magic. In contrast with this familiar piece of magic, the formation of one pendant catenane spurs on the formation of its nearest neighbors to the extent that once the process is underway, there is no stopping it: it keeps going until every blue ring is catenated by a red one. The catenation process is accompanied by extensive changes in the shape of the polymer chains which not only get a fillip from the catenanes stacking up next to each other along the chains of the molecule, but also become interdigitated with other molecules in the vicinitiy.

Programmed self-assembly of metal nanoparticles can be achieved by utilizing the concept of molecular recognition — between p-electron rich 1,5-dioxynaphthalene (DNP) as the guest and p- electron deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) as the host — to form hybrid nanowires. The idea here is to prepare a homopolymer, based on DNP units by utilizing “click” reaction, which will be the binding motif for the CBPQT4+ ring, attached to gold nanoparticles. Upon mixing, a complementary Donor-Ac-ceptor-Donor-Donor (DADA) stack between the CBPQT4+ ring and the DNP subunits are expected to make the polymer threads attain a folded conformation in order to maximize the p-p interaction with the bipyridinium (BIPY2+) subunits in the CBPQT4+ ring, thus forming 1D nanoparticle arrays. In order to demonstrate the proof-of-principle, we have recently synthesized well-defined oligomers of the DNP subunits, and studied their complexation behavior with the CBPQT4+ ring. In addition, we have also prepared five different rotaxanes — all of which have provided an evidence of a three-dimensionally folded morphology. These hybrid materials will be of particular interest to materials scientists for the development of stimuli responsive smart materials.

Single crystals of MOF-5 and a new “green” MOF composed of common alkali metal salts and gamma-cyclodextrin called CD-MOF are grown on the millimeter scale.  The crystals, once they’ve grown in solution for 3–5 days, are collected and rinsed.  They are then placed on an agarose gel which has been impregnated with dyes.  If stamping specific patterns is the goal, the agarose is soaked with a single dye compound, like Neutral Red and the crystal are allowed to rest upon the gel for 5–10 minutes until the dye has diffused into the crystal.   The dyes, once soaked into the crystal, can then be manipulated by external stimuli to change their adsorption properties. If separation is the goal, a mixture of compounds will be impregnated into the gel and the crystal is set upon the gel for upwards of 30 minutes while the two dyes diffuse through the crystal at different rates. It is possible to perform chromatography in single MOF crystals.

In order to harness useful energy on a macroscopic scale, the molecular movements of the muscle-like molecules should be significant enough so that the accumulated contraction /extension movements of an assembly of these molecules are large enough to be monitored and harnessed. In this context, we have designed and synthesized a new [c2]daisy chain monomer which will exert a better contraction/extension ratio, compared to what has already been reported in the scientific literature. Such improved contraction/extension behavior originates from the 1,2-diphenylethynyl spacer between the two recognition sites. It is rigid and is longer than the phenyl spacer in the previously reported [c2]daisy chain systems. We are currently amplifying the preparation in order to produce a large quantity of the [c2]daisy chain materials. In the future, we plan to polymerize this compound with a library of different linkers — with functional groups such as thiourea, dialkynene, dithiol, dialdehyde or diamine — to form a collection of structurally diverse linear polymers. These polymer chains, depending on the nature of their linkers, may undergo noncovalent or covalent self-assembly and hence form ordered polymer chain bundles. Upon achieving the synthesis and characterization of self-assembled, organized muscle-like polymer clusters, we aim to induce molecular motion in the [c2]daisy chain moiety in the clusters and to achieve materials actuation on the microscopic and, eventually, on the macroscopic level.

Rotacatenanes are exotic molecular structures which can be visualized as a unique combination of a [2]catenane and a [2]rotaxane, thereby combining both the circumrotation of the ring component (rotary motion) and the shuttling of the dumbbell component (translational motion) in one structure. This research demonstrates the power of constructing complex molecular machines using template-directed protocols, enabling us to make the transition from simple molecular switches to their multistate variants for enhan-cing information storage in molecular electronic devices. The detailed study of the switching mechanism of this new type of mechanically interlocked molecules (MIMs) has demonstrated that additional stable states comprising tetrathiafulvalene (TTF) radical p-dimer inter-actions — which have been utilized in various electrical, magnetic, and optical materials — can be incorporated into MIMs. Furthermore, the stability of the TTF radical p-dimer interactions can even be modulated by changing the components of these architectures. Switchable rotacat-enanes, capable of hosting radical interactions, are promising mechanostereochemical candidates for exploring applications in molecular electronics and spintronics.

Metal–organic frameworks (MOFs) are extensive in number and promise widespread applications. In order to add complexity to their structures in a controlled manner, we have already shown that organic struts bearing components of mechanically interlocked molecules (MIMs), such as crown ethers, pseudorotaxanes, and catenanes, can be reticulated into 3D MOFs, and anchored at precise locations and with uniform relative orientations throughout the framework. In principle, molecular machinery mounted as integrated components in “robust” MOFs, are capable of “dynamics” without compromising the fidelity of the entire system. One can easily conceptualize a chemical world where chameleon-like MOF crystals can be induced under the influence of chemicals (pH change), electricity (redox change) and light to travel in solution from one environment to another. The ability to build such integrated systems that are capable of a complex set of functions is reminiscent of operations in the biological world. Robust dynamics, therefore, is about concept transfer from the life sciences into the chemistry of materials.

The goal of this project is to arrange prototype molecular machines inside of an inorganic framework in order to access the properties of these molecules working in parallel. Non-equilibrium processes that drive the molecular machinery could be used to transform energy from one from to another.

Two donor−acceptor [3]catenanes-composed of a tetracationic molecular square, cyclobis(paraquat-4,4´-biphenylene), as the π-electron deficient ring and either two tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) containing macrocycles or two TTF-butadiyne-containing macrocycles as the π-electron rich components - have been investigated in order to study their ability to form TTF radical dimers. It has been proven that the mechanically interlocked nature of the [3]catenanes facilitates the formation of the TTF radical dimers under redox control, allowing an investigation to be performed on these intermolecular interactions in a so-called "molecular flask" under ambient conditions in considerable detail. In addition, it has also been shown that the stability of the TTF radical-cation dimers can be tuned by varying the secondary binding motifs in the [3]catenanes. By replacing the DNP station with the butadiyne group, the distribution of the TTF radical-cation dimer can be changed from 60% to 100%. These findings have been established by several techniques including cyclic voltammetry and UV-Vis-NIR and EPR spectroscopies, as well as with X-ray diffraction analysis which has provided a range of solid-state crystal structures. The results are also supported by high-level DFT calculations. The findings contribute significantly to our fundamental understanding of the interactions within the TTF radical dimers.

This is the project of hybrid Fe₂O₃-Pd nanoparticle photocatalysts. The bottom images are TEM images of hybrid Fe₂O₃-Pd NPs we prepared. Fe₂O₃ is a type of stable semiconducting materials and both Fe and oxygen are naturally abundant elements, so Fe₂O₃ is expected as potentially robust and inexpensive photocatalysts. However, the slow charge transfer and the high probability of charge recombination of Fe₂O₃ limit them as effective photocatalysts. Here, our idea is to use metal nanoparticle domain as co-catalysts to help the electron transfer, improve the charge separation and suppress the charge recombination, and so to enhance the photocatalytic activity of Fe₂O₃ domain. We used TEA as sacrificial agents to quench the holes generated at Fe₂O₃ domain and the electrons transferred to Pd domain would reduce Ag salt to Ag nanoparticles. The enhanced photocatalytic activity of hybrid Fe₂O₃-Pd NPs was proved by the higher concentration of formed Ag nanoparticles.