Building Blocks for the Assembly of Nanostructures
The natural world and many man made technologies are driven by self-assembly, involving the autonomous organization of individual components as a result of specific local interactions into functional structures. Self-assembly is a platform from which to construct materials with a high complexity, in high precision, with an inbuilt error- correction system due to its dynamic nature. For example, in nature this principle allows us to encode our genome by the controlled opening and closing two stands of DNA. In addition, linear protein chains fold into elaborate 3D structures for specific functions, cells assemble and divide for example into embryonic tissue and form the basis of reproduction. In fact, all these biological components have a high degree of organization owing to specific interactions at molecular level. The principle of self- assembly is also used in technology for example for drug delivery through liposomes made out of lipid bilayers to carry the drug through membranes to reach specific tissues. It is also the basis of many type of biosensors, such as glucose sensors used by diabetics to monitor their blood sugar level. But also future computer based technology may need ordered arrays of molecules, such as rotaxanes. Rotaxanes for example assemble and switch between two states, which is a promising step towards future molecular-based computers. Indeed, society is in a demand for more powerful computers and therefore its working components ideally need further miniaturization.
This thesis is focusing on different aspects of the self-assembly. The molecular level, the design of new molecules for the self-assembly on surfaces. We designed several molecules and dyes, such as terpyridines, rhodamines and photolabile molecules, which assemble on metal surfaces. Another aspect of this thesis is the testing and evaluating for possible application, such as in biosensing on surfaces with photolabile compounds. Furthermore, the complex strengths of osmium cations and terpyridin was determined using terpyridine molecules assembled on an AFM tip and on a metal surface. Moreover, a plasmon-exciton hybrid was observed by assembling rhodamine dyes on metal nanostructures. Spectral dips in the scattering spectrum appear due to strong coupling between the molecule and the metal. A third aspect of this work was the synthesis of nanoparticles and its assembly into discrete aggregates such as dimers using different approaches, such as molecular linkers or electrostatic interaction. Heterodimeric NPs were tested in hydrogen uptake experiments on individual particles.