Self-assembled monolayers and patterned surfaces derived from them as templates for the growth of chiral crystals

Resumen

El proyecto de investigación presentado en esta Tesis titulada ¿Self-assembled monolayers and patterned surfaces derived from them as templates for the growth of chiral crystals¿, tiene como principal objetivo establecer el efecto de las monocapas auto-ensambladas (SAMs) quirales en la nucleación y crecimiento cristalino de compuestos orgánicos, y encontrar las condiciones ideales para favorecer la nucleación heterogénea y su consecuente crecimiento cristalino. La investigación realizada detalla el estudio realizado para conseguir la cristalización controlada sobre superficies funcionalizadas de determinados compuestos quirales y sales diastereoméricas. Para ello se realizaron estudios de cristalización de mencionados compuestos sobre diferentes superficies funcionalizadas. El estudio de la cristalización controlada sobre superficies funcionalizadas comienza por la funcionalización de dicha superficie con phencyphos 4-metilentiol, la cual proporcionara resultados muy prometedores debido a su influencia, demostrada en esta tesis, sobre el proceso de cristalización. La cristalización de phencyphos sobre SAMs de este compuesto, no es controlada y presenta diferentes orientaciones. El disolvente es crucial ya que tiene una enorme influencia en el proceso, según el disolvente empleado en la cristalización de phencyphos sobre superficies funcionalizadas, en el caso de usar isopropanol se obtienen los cristales ramificados, un crecimiento muy peculiar. El método conocido como impresión por microcontacto (microcontact printing en inglés) ofrece un sistema en la superficie que permite favorecer el transporte de masa hacia la zona deseada de la superficie. Las cristalizaciones sobre superficies micropaternadas, tanto de phencyphos como de la sal diastereomérica (p-metilphencyphos y feniletilamina) se han conseguido controlar tras un estudio detallado del efecto del disolvente, el tiempo de la superficie en la disolución, la forma del patrón en superficie, los tioles combinados en superficie y la velocidad de evaporación The research presented in this Thesis entitled Self-assembled monolayers and patterned surfaces derived from them as templates for the growth of chiral crystals has as the main objective of the establish the effect of chiral self-assembled monolayers (SAMs) on the nucleation and the crystal growth of organic compound, and find conditions which favour heterogeneous nucleation and subsequent growth. The possibility to control crystallization processes using self-assembled monolayers is an extremely interesting and promising approach in organic materials. This control has achieved by the use of inorganic crystalline substrates where nucleation is induced via epitaxy, although organic single crystals and SAMs have been used to control the polymorphic selectivity of the compound to crystallize, which is based on the lattice match between the molecular cluster and crystalline substrate terraces. According to this concept, SAMs have been used as controlled nucleation centres. This research describes the study in order to achieve the controlled crystallization of the compound phencyphos and diastereomeric salts on functionalized surfaces, and shows the differences between homogenous SAMs and combined SAMs (Microcontact printing method). The controlled crystallisation study starts with the formation of SAMs on gold with a novel chiral thiol, which has potential for nucleating crystal growth, (phencyphos 4-methylenthiol, PMT), and the crystallisation of phencyphos on them. The functionalisation of gold with monolayers of this compound has provided significant results due to its demonstrated influence in the crystallisation process. Thus, the successful functionalisation of the gold substrate by this resolving agent type molecule provided the chiral property to the self-assembled monolayer on gold. Phencyphos crystallises on PMT monolayer following different orientations and grow off the surface; depending on the solvent used these crystals grow as branched crystals (in isopropanol) on the functionalised surface. The microcontact printing method favours the mass transport to the desired thiol, minimizing evaporation effect at small scale. The surface combined of PMT and dodecanethiol has been the key for the development of surfaces which can induce the nucleation process on surface. On micropatterned surfaces, phencyphos crystallizes following a preferential orientation. Crystal growth is highly depending on the solvent used to crystalize phencyphos. The same enantiomer of phencyphos crystallized in different solvent (Chloroform and Isopropanol), yield different crystal growth, because the heterogeneous nucleation is effective when the solvent is allowed to evaporate slowly from the surface, allowing good mass transport to the desired regions. The diastereomeric salt most studied and presented here is the one formed by a phencyphos derivate, p-methyl phencyphos which provides a pair of crystalline salts with chiral amines. X-ray crystal structure of this diastereomeric salt reveal 10-membered rings constructed through hydrogen bonds, in which two ammonium groups formally replace phencyphos molecules seen in the phencyphos hydrate structure. The hydrogen bonds are strong and provide several polar faces to the crystalline structure, thus diastereomeric salts should have their crystals templated easily on polar SAM. There are several parameters that also have a dramatic influence on the crystallisation process such as the pattern shape and size which are critical. Thus the motif size which presents better results of favour the nucleation is for dots of 5 µm diameter spaced by 10 µm, for both crystallisation systems. The Dutch resolution has been also studied on micropatterned surfaces. The complexity of the family type crystallisation will require the development of specific additives to favour heterogeneous nucleation.