Photoswitching Using Visible Light: A New Class of Organic Photochromic Molecules

A versatile new class of organic photochromic molecules that offers an unprecedented combination of physical properties including tunable photoswitching using visible light, excellent fatigue resistance, and large polarity changes is described. These unique features offer significant opportunities in diverse fields ranging from biosensors to targeted delivery systems while also allowing non-experts ready synthetic access to these materials

Directed Self-Assembly of Metallosupramolecular Polymers at the Polymer–Polymer Interface

Directed self-assembly of a metallosupramolecular polymer is achieved at the interface between two polymer films by simple melt pressing. Blends of a 2,6-bis­(<i>N</i>-methylbenzimidazolyl)­pyridine (MeBip) side-chain functionalized polystyrene in a polystyrene matrix and Zn­(NTf₂)₂ in a poly­(methyl methacrylate) matrix were pressed together above the <i>T</i>_g of the matrix polymers resulting in diffusion of the components and subsequent self-assembly of the metallosupramolecular polymer at the polymer–polymer interface. The formation of the metallosupramolecular polymer was monitored by spectroscopy and microscopy and it was found that the interfacial self-assembly occurs at the processing temperatures (ca. 210 °C) within 5 min. It was further shown that this materials system resulted in robust films that exhibited a new emergent property, namely, phosphorescence, which is not exhibited by any of the individual components nor the metallosupramolecular polymer itself

Influence of Metal Ion and Polymer Core on the Melt Rheology of Metallosupramolecular Films

Detailed rheological studies of metallosupramolecular polymer films in the melt were performed to elucidate the influence of the metal ion and polymer components on their mechanical and structural properties. 4-Oxy-2,6-bis(<i>N</i>-methylbenzimidazolyl)pyridine telechelic end-capped polymers with a low-<i>T</i>_g core, either poly(tetrahydrofuran) or poly(ethylene-<i>co</i>-butylene), were prepared with differing ratios of Zn²⁺ and Eu³⁺ to determine the influence of polymer chain chemistry and metal ion on the properties. Increasing the amount of the weaker binding europium yielded more thermoresponsive films in both systems, and results show that the nature of the polymer core dramatically affected the films mechanical properties. All of the films studied exhibited large relaxation times, and we use this to explain the pure sinusoidal behavior found in the “nonlinear” viscoelastic region. Basically, the system cannot relax during a strain cycle, allowing us to assume the network destruction and creation rates to be only a function of the strain amplitude in a simplified network model used to rationalize the observed behavior

<i>In Situ</i> Formation of Metal Nanoparticle Composites via “Soft” Plasma Electrochemical Reduction of Metallosupramolecular Polymer Films

Metallosupramolecular polymers, consisting of both inorganic and organic phases, offer an interesting platform for the <i>in situ</i> formation of metal nanoparticles embedded in a polymer film. Here, we report the synthesis and characterization of Pt-containing supramolecular polymers, prepared from 4-oxy-2,6-bis­(10-methylbenzimidazolyl)­pyridine end-capped polymers of either poly­(tetrahydrofuran) or poly­(ethylene-<i>co</i>-butylene), where the OMeBip:Pt complex phase separates from the macromonomer soft core to yield mechanically robust films. Exposure of these Pt-containing supramolecular polymer films to an atmospheric-pressure plasma setup results in the controlled nucleation and growth of uniformly sized, crystalline, unagglomerated Pt nanoparticles. The mechanism for nanoparticle nucleation is believed to be reduction by plasma electrons, eliminating the need for hydrogen gas or other reactive chemicals and allowing “soft” processing. We show that the size and density of the nanoparticles is modulated by the exposure time, molecular weight of the polymer core, and polarity of the polymer core, thus enabling metal nanoparticle composites to be produced in a single step

Optically healable supramolecular polymers

Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications. Most approaches to healable materials require heating the damaged area. Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal–ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal–ligand motifs and a concomitant reversible decrease in the polymers’ molecular mass and viscosity, thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light–heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries