Refine
Has Fulltext
- no (10)
Document Type
- Article (8)
- Monograph/Edited Volume (1)
- Doctoral Thesis (1)
Is part of the Bibliography
- yes (10) (remove)
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 characterized by a uniaxial texture, which is correlated with the dipping direction during deposition of the LB film.
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.
The electrochemical behaviour of new amphiphilic 1,3,4-oxadiazoles were studied by cyclic voltammetry. The influence of the supra- molecular structure on the redox behaviour in liquid or solid solutions, in Langmuir-Blodgett multilayers, and in amorphous films is investigated in detail. The reversible reduction of amphiphilic 2,5-diarylene- 1,3,4-oxadiazoles is significantly influenced by substituents in the para position of the phenylene ring. In the solid states the reduction peak potentials are shifted to more negative values compared to data measured in solution. This shift increases as the film thickness is increased. An influence of the supramolecular order in the solid films was not found. In-situ UV-vis spectroelectrochemistry of LB-multilayers deposited onto indium tin oxide (ITO) glass give evidence for the formation of radical anions in the highly ordered layer.
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.
Different aspects of the structure formation for a class of molecules containing the diphenyl-1,3,4-oxadiazole fragment are discussed. Starting from the bulk state with the ideal crystal lattice and the derivation of some common packing motifs the formation of liquid-crystalline states are described. This leads to the consideration of structures found in Langmuir-Blodgett films and those obtained by organic molecular beam deposition. These structures may again be compared to those for the bulk crystalline state. Common features as well as characteristic differences due to peculiarities of the individual molecular structures are discussed. (c) 2005 Elsevier B.V. All rights reserved