Shaker
On the way to molecular optical switches : a solid state NMR study of trans-cinnamic acids
Abstract
dc:descriptionStereospecific light-driven reactions have gained attraction because of a potential application in optical memory storage systems. This field of research is motivated by the pursuit of miniaturization of high capacity storage systems, with the conventional technique soon reaching its limits. In molecular optical storage systems, the switch between two forms of a molecule is optically activated and the two forms can be assigned to 0 and 1 in the computer code for the storage of information. With the dimensions of a single molecule, molecular electronics redefines the ultimate limit of miniaturization. Here, the design of materials for molecular switches is an essential step. Trans-cinnamic acid undergoes an optically activated and stereoselective reaction. The study presented here focuses on the [2+2] photodimerization of trans-cinnamic acid as a model system for optical storage materials and for improving the understanding of solid-state reactions in general. In this work, the influence of polymorphism and aromatic substitution on the photoreaction of cinnamic acid is studied. For this purpose several cinnamic acid derivatives have been chosen, starting with the two photoactive cinnamic acid polymorphs, alpha and beta. Within the alpha-polymorphs, o-methoxy and o-ethoxy cinnamic acids together with unsubstituted cinnamic acid are investigated to study the effect of aromatic substitution on the ortho position with increasing substituent chain length and size. Finally, within the beta-polymorphs, o-, m- and p-bromo substituted cinnamic acids are studied to determine the effect of substitution in the different ortho, meta and para aromatic positions on the photoreaction. The [2+2] photodimerization reaction of the trans-cinnamic acids is compared using 13C solid-state NMR spectroscopic techniques with the aid of theoretical calculations of the relevant NMR parameters. The kinetics of the reaction is monitored by means of 13C cross polarization spectra under magic angle spinning and analyzed with a model, which relates the reaction constants to the dimensionality of the growth. Moreover, 13C chemical shift anisotropy tensors have been determined to get an insight into the relative orientations of carbon atoms, which is sensitive to molecular conformational changes during the reaction. The structure-directing effect of intermolecular hydrogen bonding is investigated using high-speed MAS 1H NMR spectroscopy, showing correlations between atoms of adjacent molecules.
Degree
thesis:*- Grantor dc:publisher
- Shaker
- Year dc:date
- 2008
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- da Fonseca, Isa Alexandra Queiroz
- Contributors dc:contributor
-
- Blümich, Bernhard
Subjects
dc:subject × 10Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng