Simone Radl

UV-induced modulation of the conductivity of polyaniline: towards a photo-patternable charge injection layer for structured organic light emitting diodes

In macromolecular electronics the organic material should offer—besides the desired electronic properties—the possibility of lateral patterning. Here, we report on a novel polyaniline derivative bearing photosensitive N-formamide groups. UV illumination of this polymeric material leads to a decarbonylation reaction resulting in polyaniline which can be subsequently protonated to yield the conductive emeraldine salt. Due to the fact that the conductivity depends on the conversion of the photoreaction, a selective adjustment of the conductivity by means of UV light is feasible. These photo-induced conductivity changes were corroborated in thin films by conductive AFM measurements. Further, we demonstrate the versatility of this polymer with respect to a patterned modification of the conductivity as well as its application as a photo-patternable charge injection layer for structured OLEDs. This makes the new polymer an interesting candidate for electrodes and interconnects in various organic electronic devices.

Wavelength selective refractive index modulation in a ROMP derived polymer bearing phenyl- and ortho-nitrobenzyl ester groups

Patterning and tuning of the refractive index in polymers by means of UV-light is of great interest for optical applications such as polymeric waveguides or optical data storage devices. In this contribution, we report on the synthesis of a polynorbornene based copolymer bearing ortho-nitrobenzyl and phenyl ester groups capable of undergoing the photo-induced cleavage reaction and in a subsequent step optionally the photo-Fries rearrangement upon irradiation with UV-light. The photoreaction of these aromatic ester groups was investigated by means of FTIR, UV-VIS and spectroscopic ellipsometry. Due to the difference in UV absorption of the photoreactive units, the o-nitrobenzyl ester can be selectively excited by UV-light above 300 nm, while a subsequent illumination with 254 nm induces the photo-Fries rearrangement of the remaining phenyl ester groups. The structural changes in the chemical composition upon UV illumination lead to significant changes in the refractive index of the polymeric materials. Whilst the photo-Fries rearrangement of the phenyl ester groups causes a remarkable increase in the refractive index, it was found that the photo-induced cleavage reaction of ortho-nitrobenzyl ester moieties causes a decrease of the refractive index. This fact enables a selective tailoring of the refractive index by the choice of the applied wavelength. In addition, a two-step irradiation procedure using a sequence of different wavelengths provides the possibility of erasing and even inverting the index contrast.

Versatile thiol-based reactions for micrometer- and nanometer-scale photopatterning of polymers and biomolecules

Thiol-based chemistry provides a mild and versatile tool for surface functionalization. In the present work, mercaptosilane films were patterned by utilizing UV-induced photo-oxidation of the thiol to yield sulfonate groups via contact and interferometric lithography (IL). These photo-generated sulfonic acid groups were used for selective immobilization of amino-functionalized molecules after activation with triphenylphosphine ditriflate (TPPDF). Moreover, protein-resistant poly(oligoethyleneglycolmethacrylate) (POEGMA) brushes were grown from the intact thiol groups by a surface-induced polymerization reaction. Exploiting both reactions it is possible to couple amino-labelled nitrilotriacetic acid (NH2-NTA) to sulfonate-functionalized regions, enabling the site-specific binding of green fluorescent protein (GFP) to regions defined lithographically, while exploiting the protein-resistant character of POEGMA brushes to prevent non-specific protein adsorption to previously masked areas. The outstanding reactivity of thiol groups paves the way towards novel strategies for the fabrication of complex protein nanopatterns beyond thiol-ene chemistry.

Data on synthesis and thermo-mechanical properties of stimuli-responsive rubber materials bearing pendant anthracene groups

The photo-reversible [4πs+4πs] cycloaddition reaction of pendant anthracene moieties represents a convenient strategy to impart wavelength dependent properties into hydrogenated carboxylated nitrile butadiene rubber (HXNBR) networks. The present article provides the 1H NMR data on the reaction kinetics of the side chain functionalization of HXNBR. 2-(Anthracene-9-yl)oxirane with reactive epoxy groups is covalently attached to the polymer side chain of HXNBR via ring opening reaction between the epoxy and the carboxylic groups. Along with the identification, 1H NMR data on the quantification of the attached functional groups are shown in dependence on reaction time and concentration of 2-(anthracene-9-yl)oxirane. Changes in the modification yield are reflected in the mechanical properties and DMA data of photo-responsive elastomers are illustrated in dependence on the number of attached anthracene groups. DMA curves over repeated cycles of UV induced crosslinking (λ>300 nm) and UV induced cleavage (λ=254 nm) are further depicted, demonstrating the photo-reversibility of the thermo-mechanical properties. Interpretation and discussion of the data are provided in “Design and application of photo-reversible elastomer networks by using the [4πs+4πs] cycloaddition reaction of pendant anthracene groups” (Manhart et al., 2016) [1].

The influence of surface modification on the electrical properties of silicon carbide flakes

Field grading materials with nonlinear behaviour are used in many high voltage applications to avoid any stress concentration that can deteriorate the material performance. In the present work, the current-voltage characteristics of surface functionalized silicon carbide (SiC) flakes were studied and compared to untreated particles. The nonlinear behavior of SiC flakes can be described by transport mechanisms at the grain contact, which can be modeled by Schottky-like barriers. The influence of the organic surface layer on the conduction mechanisms and the corresponding electrical properties were evaluated. In addition, physico-chemical analysis, including X-ray photoelectron spectroscopy (XPS), optical microscopy and zeta-potential measurements were accomplished in order to analyze the surface properties of the SiC flakes, prior to and after surface modification.