Correlation of Device Performance and Fermi Level Shift in the Emitting Layer of Organic Light-Emitting Diodes with Amine-Based Electron Injection Layers.

We investigate three amine-based polymers, polyethylenimine and two amino-functionalized polyfluorenes, as electron injection layers (EILs) in organic light-emitting diodes (OLEDs) and find correlations between the molecular structure of the polymers, the electronic alignment at the emitter/EIL interface, and the resulting device performance. X-ray photoelectron spectroscopy measurements of the emitter/EIL interface indicate that all three EIL polymers induce an upward shift of the Fermi level in the emitting layer close to the interface similar to n-type doping. The absolute value of this Fermi level shift, which can be explained by an electron transfer from the EIL polymers into the emitting layer, correlates with the number of nitrogen-containing groups in the side chains of the polymers.

Cell Fixation by Light-Triggered Release of Glutaraldehyde.

Chemical fixation of living cells for microscopy is commonly achieved by crosslinking of intracellular proteins with dialdehydes prior to examination. We herein report a photocleavable protecting group for glutaraldehyde that results in a light-triggered and membrane-permeable fixative, which is nontoxic prior to photocleavage. Lipophilic ester groups allow for diffusion across the cell membrane and intracellular accumulation after enzymatic hydrolysis.

High-Performance Electron Injection Layers with a Wide Processing Window from an Amidoamine-Functionalized Polyfluorene.

In this work, we present organic light-emitting diodes (OLEDs) utilizing a novel amidoamine-functionalized polyfluorene (PFCON-C) as an electron injection layer (EIL). PFCON-C consists of a polyfluorene backbone to which multiple tertiary amine side chains are connected via an amide group. The influence of molecular characteristics on electronic performance and morphological properties was tested and compared to that of the widely used, literature known amino-functionalized polyfluorene (PFN) and polyethylenimine (PEI).

Emissive Polyelectrolytes As Interlayer for Color Tuning and Electron Injection in Solution-Processed Light-Emitting Devices.

Herein we present a solution-processed hybrid device architecture combining organic light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) in a bilayer architecture. The LEC interlayer promotes the charge injection from an air-stable Ag cathode as well as permits the color tuning of the device emission. To this end, we used an alcohol-soluble anionic polyfluorene derivative, the properties of which were investigated by absorption and photoluminescence spectroscopy as well as by cyclic voltammetry.

Naphthalene Tetracarboxydiimide-Based n-Type Polymers with Removable Solubility via Thermally Cleavable Side Chains.

Multilayer solution-processed devices in organic electronics show the tendency of intermixing of subsequently deposited layers. Here, we synthesize naphthalene tetracarboxydiimide (NDI)-based n-type semiconducting polymers with thermally cleavable side chains which upon removal render the polymer insoluble. Infrared and photoelectron spectroscopy were performed to investigate the pyrolysis process.

Light-Induced Solubility Modulation of Polyfluorene To Enhance the Performance of OLEDs.

Liquid-phase processing is a key prerequisite for the cost-efficient fabrication of organic electronic devices. We report an approach for light-induced modulation of the solubility of π-conjugated polymers (polyfluorene) with side chains functionalized with hydroxycinnamic acid. Irradiation with light cleaves the solubilizing side chains and renders the thin films of the polyfluorene insoluble.

A biphasic mercury-ion sensor: exploiting microfluidics to make simple anilines competitive ligands.

Combining the molecular wire effect with a biphasic sensing approach (analyte in water, sensor-dye in 2-methyltetrahydrofuran) and a microfluidic flow setup leads to the construction of a mercury-sensitive module. We so instantaneously detect Hg(2+) ions in water at a 500 μM concentration. The sensor, conjugated non-water soluble polymer 1 (XFPF), merely supports dibutylaniline substituents as binding units.

Dipolar SAMs Reduce Charge Carrier Injection Barriers in n-Channel Organic Field Effect Transistors.

In this work we examine small conjugated molecules bearing a thiol headgroup as self assembled monolayers (SAM). Functional groups in the SAM-active molecule shift the work function of gold to n-channel semiconductor regimes and improve the wettability of the surface. We examine the effect of the presence of methylene linkers on the orientation of the molecule within the SAM.

Light-induced protein dimerization by one- and two-photon activation of gibberellic acid derivatives in living cells.

We developed a highly efficient system for light-induced protein dimerization in live cells using photo-caged derivatives of the phytohormone gibberellic acid (GA3 ). We demonstrate the application of the photo-activatable chemical inducer of dimerization (CID) for the control of protein translocation with high spatiotemporal precision using light as an external trigger. Furthermore, we present a new two-photon (2P)-sensitive caging group, whose exceptionally high two-photon cross section allows the use of infrared light to efficiently unleash the active GA3 for inducing protein dimerization in living cells.

Emission turn-on and solubility turn-off in conjugated polymers: one- and two-photon-induced removal of fluorescence-quenching solubilizing groups.

The synthesis of highly efficient two-photon uncaging groups and their potential use in functional conjugated polymers for post-polymerization modification are reported. Careful structural design of the employed nitrophenethyl caging groups allows to efficiently induce bond scission by a two-photon process through a combination of exceptionally high two-photon absorption cross-sections and high reaction quantum yields. Furthermore, π-conjugated polyfluorenes are functionalized with these photocleavable side groups and it is possible to alter their emission properties and solubility behavior by simple light irradiation.

Soluble diazaiptycenes: materials for solution-processed organic electronics.

The synthesis and characterization of soluble azaiptycenes is reported. Optical and physical properties were studied and compared with those of the structurally consanguine azaacenes. Electrochemical experiments and quantum-chemical calculations revealed the electronic structure of the iptycene derivatives.

Processing follows function: pushing the formation of self-assembled monolayers to high-throughput compatible time scales.

Self-assembled monolayers (SAMs) of organic molecules can be used to tune interface energetics and thereby improve charge carrier injection at metal-semiconductor contacts. We investigate the compatibility of SAM formation with high-throughput processing techniques. Therefore, we examine the quality of SAMs, in terms of work function shift and chemical composition as measured with photoelectron and infrared spectroscopy and in dependency on molecular exposure during SAM formation.

The compromises of printing organic electronics: a case study of gravure-printed light-emitting electrochemical cells.

Light-emitting electrochemical cells (LECs) are fabricated by gravure printing. The compromise between device performance and printing quality is correlated to the ink formulation and the printing process. It is shown that the rheological properties of the ink formulations of LECs can be tailored without changing the chemical composition of the material blend.

From thia- to selenadiazoles: changing interaction priority.

The synthesis, optical, and electrochemical properties as well as solid-state structures of a series of alkynylated, benzannulated selenadiazoles are reported. This set of compounds is compared to the lighter homologue series, the thiadiazoles. The selenadiazoles show head-to-head dimerization in the solid state, while packing of the thiadiazoles was dominated by the steric bulk of the side groups.

Thiadiazoloquinoxalines: tuning physical properties through smart synthesis.

The synthesis of π-conjugated acceptors based on thiadiazoloquinoxaline (TQ) derivatives is described. Apart from reporting on the functionalization of the TQ core, the influence of the substituents was studied by UV-vis absorption and emission spectroscopy, cyclic voltammetry measurements, and DFT calculations. By changing the donor as well as the π-spacer, a fine-tuning of the photo- and electrochemical properties was achieved.

Photocatalytic hydrogen evolution through fully conjugated poly(azomethine) networks.

Three-dimensional conjugated poly(azomethine) networks were found to be promising candidates for applications in photocatalytic water splitting. Straightforward synthetic protocols lead to fully organic photocatalysts that showed enhanced long-time stability. Furthermore, the catalytic performance of these materials was correlated to the molecular composition and the optoelectronic properties of the samples.