Patrick J. Baesjou

Dopant density determination in disordered organic field-effect transistors

We demonstrate that, by using a concentric device geometry, the dopant density and the bulk charge-carrier mobility can simultaneously be estimated from the transfer characteristics of a single disordered organic transistor. The technique has been applied to determine the relation between the mobility and the charge density in solution-processed poly(2,5-thienylene vinylene) and poly(3-hexyl thiophene) thin-film field-effect transistors. The observation that doping due to air exposure takes place already in the dark, demonstrates that photoinduced oxygen doping is not the complete picture.

A kinetic and spectroscopic study on the copper catalyzed oxidative coupling polymerization of 2,6-dimethylphenol. X-ray structure of the catalyst precursor tetrakis(N-methylimidazole)bis(nitrato)copper(II)

The complex of copper(II) nitrate with N-methylimidazole (Nmiz) ligand has been studied as a catalyst for the oxidative coupling of 2,6-dimethylphenol by means of kinetic and spectroscopic measurements. The order of the reaction in copper is fractional and depends on the N/Cu ratio and the base/Cu ratio, indicating that there are at least two possible rate-determining steps, i.e. the formation of a dinuclear copper species and the phenol oxidation. EPR spectroscopy performed on frozen solutions with varying ligand to copper ratios shows that all Cu(II) is converted into the precursor complex at a ratio of 4 to 1, whereas in kinetic experiments, maximum activity and selectivity are reached only at a ratio of at least 30 to 1. Base is needed as a co-catalyst, and the maximum reaction rate is reached at a base to copper ratio of 1.8 to 1. The solid-state X-ray structure of the catalyst precursor complex has been determined to be [Cu(Nmiz)(4)(NO3)(2)], monoclinic, space group P2(1)/n, a=8.452(1)Angstrom, b=10.376(2)Angstrom, c=12.821(2)Angstrom, beta=94.88(2)degrees, Z=1, R=0.049 for 3525 reflections. This structure consists of an axially elongated octahedral CuN4O2 chromophore, which is in agreement with frozen-solution EPR spectra. Investigations under conditions where water and dioxygen were carefully excluded, have shown that for the phenol oxidation step the presence of dioxygen is not required. However, the reaction does require a trace of water (or hydroxide) to form the reactive intermediate. A modified reaction mechanism for the oxidative coupling is presented with special attention to the first steps of the reaction and the equilibrium species present in solution. The role of dioxygen appears to be only to reoxidize the formed Cu(I) species and to regenerate base.

A kinetic study of the copper-catalysed oxidative coupling of 2,6-dimethylphenol. The role of copper, base and phenol concentrations

The influence of varying concentrations and ratios of phenol, base and copper on the copper/N-methylimidazole catalysed oxidative coupling of 2,6-dimethylphenol (DMP) has been studied. The reaction obeys simple Michaelis-Menten kinetics with respect to the phenol. The amount of DPQ formed during the reaction increases linearly with the increasing initial amount of DMP. At higher base-to-copper ratios an oxidative coupling experiment takes longer to complete, despite higher initial rates, which is probably due to the formation of inactive copper hydroxide species in the later stages of the reaction. The phenol oxidation step is most likely the rate-determining step, and the fractional reaction orders in copper are determined by the position of the equilibrium between mono- and dinuclear copper species, the latter being the active one

Tuning the Lattice Parameter of InxZnyP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Colloidal quantum dots (QDs) show great promise as LED phosphors due to their tunable narrow-band emission and ability to produce high-quality white light. Currently, the most suitable QDs for lighting applications are based on cadmium, which presents a toxicity problem for consumer applications. The most promising cadmium-free candidate QDs are based on InP, but their quality lags much behind that of cadmium based QDs. This is not only because the synthesis of InP QDs is more challenging than that of Cd-based QDs, but also because the large lattice parameter of InP makes it difficult to grow an epitaxial, defect-free shell on top of such material. Here, we propose a viable approach to overcome this problem by alloying InP nanocrystals with Zn(2+) ions, which enables the synthesis of InxZnyP alloy QDs having lattice constant that can be tuned from 5.93 Å (pure InP QDs) down to 5.39 Å by simply varying the concentration of the Zn precursor. This lattice engineering allows for subsequent strain-free, epitaxial growth of a ZnSezS1-z shell with lattice parameters matching that of the core. We demonstrate, for a wide range of core and shell compositions (i.e., varying x, y, and z), that the photoluminescence quantum yield is maximal (up to 60%) when lattice mismatch is minimal.

Novel concept for full‐color electronic paper

— Despite a steep increase in commercial devices comprising paper-like displays, a much desired feature is still missing: bright full-color electronic paper. A new reflective-display technology has been developed to solve this issue. For the first time, the principles behind this in-plane electrophoretic technology will be presented, which enables the realization of full-color reflective displays with a higher brightness than presently available e-paper technologies, without compromising paper-like properties such as viewing angle and ultra-low power consumption. An additional major advantage (e.g., for future low-cost manufacturing) is that, besides direct-drive and active-matrix configurations, a passive-matrix option with analog gray levels has been successfully developed.

A dinuclear copper(II) macrocyclic pyrazole compound catalyses the oxidative polymerisation of 2,6-dimethylphenol

Abstract The single crystal X-ray structure of the compound [Cu2(EtPy24Pz)(NO3)2](NO3)2(H2O)7, with EtPy24Pz is 10,24-di(pyridin-2-ylethyl)-1,5,10,15,19,24,29,30,31,32-decaaza-6,14,20,28-tetramethyl)-pentacyclo-[24.2.1.15,8.112,15.119,22]dotriaconta-6,8(30),12(31),13,20,22(32),26(29),27-octaene, shows the copper(II) ions in a square pyramidal N4O environment, crystallographically related by a twofold axis, at a distance of 7.24 A. EPR data provide evidence that the two copper (II) ions, enclosed in the macrocyclic ligand, can be brought closer together by bridging anions. A similar cooperation with the binding of dehydronated 2,6-dimethylphenol is considered to take place to incite the two-electron transfer which leads to the production of polyphenylene ether through the intermediate formation of a phenoxonium cation.

Structure of aqua-bis(ethylenediamine)copper(II) bis(2,6-dimethylphenolate)

Abstract The single-crystal X-ray structure of [Cu(en)2(H2O)](dmp)2 (en=1,2-diaminoethane and dmp=2,6-dimethylphenolate) shows the copper(II) ion in a quite regular square pyramidal N4O environment. The phenolate is not coordinated to the metal ion. Instead, the oxygen atom of each of the phenolate anions participates in three hydrogen bonds to the H atoms of the coordinated water and ethylenediamine ligands. These hydrogen atoms connect the cations and the anions in infinite polymeric chains, thereby apparently preventing the copper ions from reduction by dmp.

Optical performance of in-plane electrophoretic color e-paper

— Several e-paper technologies are currently under development with the ultimate goal of replacing printed ink on paper. Here, optical performance measurements on monochrome in-plane electrophoretic e-paper devices with unsurpassed brightness, contrast, and viewing-angle performance are reported. The measurement results are captured in a straightforward optical model that allows extrapolation to full-color performance. It demonstrates that in-plane electrophoretic color e-paper technology has the unique potential to deliver on the high standards required by digital-signage applications.

Shape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum Dots

Semiconductors are indispensable as the active light-emitting element in many optoelectronic devices. However, even the purest bulk semiconductors suffer from considerable nonradiative recombination leading to low photoluminescence efficiencies. Zero-dimensional quantum dots show a much better carrier-to-photon conversion caused by confinement of the excitons but suffer from nonradiative recombination when assembled into a solid, due to exciton energy transfer. Here, we report on the shape-dependent optical properties of self-assembled supraparticles composed of CdSe/multishell nanocrystals. All supraparticles show stable and bright photoluminescence in ambient up to high excitation intensities. When the supraparticles are deposited on a silicon surface their spherical shape is deformed due to drying. In addition to single-exciton emission, we observe bright emission from multiexciton states at high excitation powers. In contrast, supraparticles that retain their perfectly spherical shape show a spectrum with sharp Mie whispering gallery modes, while multiexciton emission is absent.

46.1: Invited Paper: Novel Design for Full‐Color Electronic Paper

Despite a steep increase in commercial devices comprising paper-like displays, a much desired feature is still missing: bright full-color electronic paper. We have developed a new reflective display technology to solve this issue. for the first time we will report about the principles behind our in-plane electrophoretic technology, which enables the realization of full-color reflective displays with a higher brightness than all present e-paper technologies, without compromising paper-like properties like viewing angle and ultra-low power consumption. An additional major advantage (e.g. for future low-cost manufacturing) is that, besides direct-drive and active-matrix configurations, a passive-matrix option has been developed successfully.