Gerald Knochenhauer

Self-assembled monolayers of novel azobenzenes for optically induced switching

Abstract Two novel azobenzenethiols containing either a sulfonamide or an amide group were synthesised and their ultrathin films were prepared by self-assembling (SA) technique. The structure of the SA monolayer (SAM) was characterised by atomic force microscopy (AFM). The switching between trans- and cis-configuration was observed by measuring the surface potential using the Kelvin probe technique while alternating irradiating the SAM with ultraviolet and visible light. A repeated switching of SAMs of 4′-(8-mercapto-octamethyleneoxy)-4-(butyl-amino-sulfonyl)azobenzene on gold with changes of the surface potential by 20 mV was observed.

Self-assembled monolayers of azobenzene functionalized 1,3,5-triazine-4,6-dithiols

Two novel azobenzene-functionalized 1,3,5-triazine-4,6-dithiols were synthesized and their ultrathin films were prepared by self-assembling (SA) technique. The switching between trans-and cis-forms was observed by measuring the surface potential using the Kelvin probe technique while alternating irradiation the SA monolayer (SAM) with ultraviolet or visible light.

Raman and i.r. spectroscopic investigation of aromatic 1,3,4-oxadiazole polymers and oligomers

Abstract The molecular structure of poly( p -phenylene-1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the α- and β-POD forms that are most obvious in the spectral region between 1500 and 1650 cm −1 . The spectra for dimer and tetramer compounds already show the same features as found for longer chains. Based on molecular modelling calculations these differences are assigned to cis and trans conformations of the main chain segments. High pressure measurements show a linear shift of the Raman lines and support the result of the thermodynamic stability of the trans conformation.

Supramolecular structures formed from heterocyclic aromatic molecules

This paper describes the formation and structure investigation of Langmuir monolayers and Langmuir-Blodgett multilayers formed from amphiphilic derivatives of 2,5-diphenyl-1,3,4-oxadiazole. The 2,5-diphenyl-1,3,4-oxadiazole group as a functional unit with interesting physical and chemical properties is maintained, while the head group, the length of the alkyl chain and the structure of the coupling unit between aromatic and aliphatic part of these linear short-chain amphiphiles is systematically varied in order to explore the influence of this change on the film forming properties and the stability of Langmuir and Langmuir-Blodgett films. Molecular mechanics simulations are shown by these systematic variations to be suitable for the prediction of optimal chemical structures allowing for a stable stratified molecular packing. The combination of a detailed structure investigation of the multilayers based on scanning force microscopy and X-ray data with molecular mechanics simulations yields an insight into the packing of the molecules and the intermolecular interactions.

Structure of thermally treated oxadiazoleamide Langmuir-Blodgett films

Abstract The thermal treatment of Y-type Langmuir-Blodgett (LB) films formed from the amphiphilic derivative of 2,5-diphenyl-1,3,4-oxadiazole 1 results in changes of the molecular packing. These changes have been analysed by a combination of X-ray specular reflectivity data, X-ray grazing incidence diffraction data and scanning force microscopy images. On the basis of these experimental data we have simulated possible supramolecular structures. These simulations provide insight into the intermolecular interactions giving rise to the observed structural transitions. The crystalline structure induced by thermal treatment of the LB films is chracterized by a uniaxial texture, which is correlated with the dipping direction during deposition of the LB film.

Supramolecular structures of aromatic 1,3,4-oxadiazole solids

Abstract Aromatic 1,3,4-oxadiazoles offer the possibility to construct new microelectronic devices due to their thermostability and their optical and electronic properties. In this paper a summary is presented of our previous results in determination of the supramolecular structure of thin poly(p-phenylene-1,3,4-oxadiazole)s (POD) films as well as of the crystal structures of low molecular weight aromatic 1,3,4-oxadiazoles. The use of a nitroalkane/Lewis acid mixture as a new solvent system for POD allows for the first time the preparation of thin POD films with a high degree of molecular order. It was also shown that these films can be electrochemically doped to obtain an electrically conducting polymer. The crystal structures of 2,5-di(tolyl)-1,3,4-oxadiazole (DTO) and 2,5-di(p-methoxycarbonyl-phenylene)-1,3,4-oxadiazole (DMPO) were determined by X-ray scattering, polarized FTIR spectroscopy and AFM. Whereas in DMPO the interactions of carbonyl groups are important for the crystallization process, the crystal growth in DTO is determined predominantly by the interactions between the aromatic rings.

Do perfluorinated chains always have to be twisted

Short perfluorinated carbon chains do not take on a helical structure when they are closely packed.

Vacuum deposition films of oxadiazole compounds: formation and structure investigation

Abstract The search for alternative routes of organic thin film formation is stimulated by the outstanding properties of these films in such fields as nonlinear optics, photonic data processing and molecular electronics. The formation of highly ordered multilayer structures by thermal vacuum deposition (VD) of organic compounds is an essential step toward the application of supramolecular organic architectures in technical systems. The VD of an amphiphilic substituted 2,5-diphenylene-1,3,4-oxadiazole 1 onto silicon substrates at defined temperature was used for the formation of ultrathin films. The structural data obtained for the VD-films of oxadiazole 1 by means of X-ray reflectivity, X-ray grazing incidence diffraction and atomic force microscopy (AFM) investigations indicate the formation of well ordered oxadiazole multilayers. The structure of the VD-multilayers is compared with that of Langmuir–Blodgett (LB) films and thermally treated LB-multilayers prepared from the same compound.

Crystal Structure of 2,5-Di(4-Methoxycarbonyl-Phenyl)-1,3,4-Oxadiazole Charactrized by AFM and IR-Spectroscopy

Abstract Low molecular aromatic 1,3,4-oxadiazoles are of interest for scientists dealing with biologically active or photochemically active materials. They are also of interest as model compounds for thermostable polymers. Here, for the first time the characterization of the crystal structure of 2,5-di(4-methoxycarbonyl-phenyl)-1,3,4-oxadiazole by Atomic Force Microscopy (AFM) and IR-spectroscopy is presented. Additionally, the experimental data are interpreted by molecular modelling results. The crystallographic data known from X-ray investigations can be determined from the molecular resolved AFM pictures too. The molecular parameters of the organic crystal were also calculated by molecular modelling and agree with all experimental results. The modelling was carried out without any assumptions about the molecular or crystal structure of the oxadiazole molecule. The oxadiazole crystal was also characterized by FTIR-spectroscopy using polarized radiation. A distinct dichroism was observed for several band...

1,3,4-oxadiazole crystals under high pressure-phase transitions and properties

Abstract Two differently substituted crystalline 2,5-diphenyl-1,3,4-oxadiazole compounds are investigated in the pressure range up to 5GPa. Phase transitions are detected using Raman and X-ray investigations.