Gregory J. E. Davidson

Stretchable Light‐Emitting Electrochemical Cells Using an Elastomeric Emissive Material

Dispersing an ionic transition metal complex into an elastomeric matrix enables the fabrication of intrinsically stretchable light-emitting devices that possess large emission areas (∼175 mm(2)) and tolerate linear strains up to 27% and repetitive cycles of 15% strain. This work demonstrates the suitability of this approach to new applications in conformable lighting that require uniform, diffuse light emission over large areas.

A [2]Rotaxane Flip Switch Driven by Coordination Geometry†

A molecular switch that is derived from a mechanically interlocked molecule (MIM) can exist in two distinct molecular arrangements: the ground-state co-conformation (GSCC) and a metastable co-conformation (MSCC), which are in equilibrium. Ideally, these co-conformers are easily identifiable by using a spectroscopic technique, their relative populations are quantifiable, and the position of the equilibrium can be controlled by some external perturbation. 2] Probably the most well understood MIM switches are the bistable [2]rotaxane, or molecular shuttle, and the bistable [2]catenane, both pioneered by Stoddart and co-workers. In these systems, two different recognition sites are present on one component for the binding of a single macrocycle. The two states of the switch are co-conformers that are related by the relative positioning of the two interlocked components. In a related set of MIMs, we recently reported the first examples of a molecular “flip switch” that operates at a single recognition site on a simple [2]rotaxane. In this system, the stability of the GSCC and MSCC are related to the degree of p stacking between the axle and the wheel, and the position of the co-conformational equilibrium was shown to be sensitive to the structure of the pyridinium component or the nature of the solvent. The flip-switch [2]rotaxane is built around the templating motif of [24]crown-8 macrocycles and 1,2-bis(pyridinium)ethane axles. This motif has been successfully used in creating a variety of unique rotaxanes and catenanes, and has been incorporated into metal–organic frameworks (MOFs). The concept of a flip-switch [2]rotaxane is shown in Scheme 1. In the [2]rotaxanes [(1)(N24C8)] and [(1)(BN24C8)], although the axle 1 is symmetrical, the two ends of the molecules are different because the crown ethers contain two different aromatic rings. This result is clearly shown by low-temperature H NMR spectra in CD2Cl2, which show eight distinct sets of pyridinium protons for [(1)(N24C8)] and six sets for [(1)(BN24C8)] because the pyridinium protons experience different amounts of shielding from the presence or absence of a naphtho or benzo ring. Each pair of exchanging resonances is separated by approximately 0.35 ppm, which is consistent with the effects of shielding that arise from p stacking. The rate of end-to-end exchange or “flipping” was determined to be on the order of 10 s 1 at room temperature. Since the flip-switch equilibrium is dictated by the degree of p stacking and thus the structural composition of the pyridinium component, it was of interest to use this principle to control the switching process. Herein, we report that the relative co-conformational stabilities can be controlled by manipulating the coordination geometry of an appended chelating group. The pioneering work of Sauvage and coworkers on Cu/Cu rotaxane systems, and Leigh and coworkers on Cu and Pd molecular shuttle systems are examples in which co-conformational switching of interlocked molecules has been shown to be dependent on metal– ligand coordination. This new [2]rotaxane flip switch system incorporates a terpyridine (terpy) group on one end of the axle (see Scheme 2). The [2]rotaxane ligands [(3)(BN24C8)] and [(3)(N24C8)] were prepared by stoppering the 1,2-bis(pyridinium) axle 2 with tert-butylbenzylbromide in the presence of an excess of the appropriate crown ether. The products were purified by column chromatography on silica and the anion was exchanged to the triflate (CF3SO3 ; OTf) salt to maintain solubility in organic solvents. The Pt and Ru complexes of these ostensibly terpy ligands were then prepared using standard conditions and appropriate starting materials (Scheme 2). We chose to prepare the square-planar complexes [PtMe(3)(BN24C8)] and [PtMe(3)(N24C8)] as well as Scheme 1. [2]Rotaxanes such as [(1)(N24C8)] or [(1)(BN24C8)] (shown) with a single recognition site but containing a crown ether with two different aromatic groups (BN24C8= [24]crown-8 bearing naphtho and benzo units; N24C8= [24]crown-8 bearing only naphtho units). The crown ether undergoes a dynamic reorientation, reminiscent of a mechanical flip switch.

Host-guest interactions template: the synthesis of a [3]catenane.

Formation of a [3]catenane containing dibenzo-24-crown ether wheels and a large dipyridiniumethane ring is templated by formation of a host-guest adduct between the [3]catenane and the external crown ether.

Selectively Metallized Polymeric Substrates by Microcontact Printing an Aluminum(III) Porphyrin Complex

We report a simple, low-cost method for the fabrication of copper wires and contacts on a wide range of flexible, rigid, and inert polymeric substrates. This method relies on procedures to oxidize the polymeric substrates to form surface-bound carboxylic acid groups. Patterning of an aluminum porphyrin ink using microcontact printing results in the formation of an aluminum porphyrin monolayer that is covalently anchored to the oxidized polymer surface via an aluminum-carboxylate bond. We characterize this monolayer using ultraviolet-visible absorption spectra, reflection-absorption infrared spectroscopy, and contact angle measurements. Patterned aluminum porphyrin monolayers bind a Pd/Sn colloidal catalyst from solution that subsequently initiates the selective deposition of copper in an electroless plating solution. We demonstrate the fabrication of patterned copper films on a variety of both flexible and rigid polymers with minimum feature sizes of 2 microm over 2 cm(2) substrates. Measurements of electrical resistivity of copper wires fabricated on flexible poly(ethylene naphthalate) (PEN) substrates as a function of the bending radius show no negative impact on electrical performance at bending radii as small as 500 microm. Permanently damaging the PEN substrate by creasing (corresponding to a bending radius of 100 microm) results in only a modest increase in resistivity.

Zwitterionic [2]rotaxanes utilising anionic transition metal stoppers

Zwitterionic [2]rotaxanes are formed when anionic [MBr3]− (M = Co(II), Mn(II)) units are used as stoppers for 1,2-bis(pyridinium)ethane/dibenzo-24-crown type axles.

Iron(II) complexes utilising terpyridine containing [2]rotaxanes as ligands

A terpyridine chelating group is incorporated into a cationic (dipyridinium)ethane axle and self-assembly synthesis used to create three [2]rotaxanes utilising 24-membered crown ether wheels: 24-crown-8, dibenzo-24-crown-8 and dinaphtho-24-crown-8 ether. The resulting [2]rotaxanes are characterised by 1H NMR spectroscopy, X-ray crystallography and mass spectrometry. The ability of these rotaxanes to act as ligands is demonstrated by the formation of bis(terpy) chelate complexes of Fe(II). The effect of using a rotaxane as a ligand is probed by UV-vis absorption spectroscopy of the Fe(II) complexes.

Templated Self-Assembly of Glass Microspheres into Ordered Two-Dimensional Arrays under Dry Conditions

This paper describes a new approach to mesoscale self-assembly in which a stream of nitrogen is used to propel micrometer-scale components toward a template of patterned liquid adhesive drops. This approach combines the use of capillary forces to hold the components in place with dry processing conditions. Eliminating the use of a liquid medium to suspend components is an important goal for mesoscale self-assembly methods because it eliminates the need for special encapsulation to protect electrically functional components. We demonstrate the dry self-assembly approach by assembling 100 microm glass microspheres into a variety of 2D patterns. A study of defects in these arrays relates parameters associated with the template--density of binding sites and volume of liquid adhesive comprising the drops--to the frequency of defects arising from the incorporation of additional microspheres into the array. Optimized template parameters and self-assembly conditions yield 2D arrays with defect rates of approximately 4-5%. We also demonstrate the versatility of this self-assembly method by producing ordered binary arrays of clear and black glass microspheres.