Carpyridines as Versatile Platforms for Shape-Assisted Self-Assembly and for Energy Transfer

Abstract

Shape, and particularly, curvature is a powerful and underexplored tool in chemical systems that will be exploited in this Thesis through different projects. To this aim, this Thesis is structured in 4 different Chapters that revolve around the same core structure: a saddle-shaped nitrogen containing macrocycle that we have termed carpyridine as a result of its constituents: carbazole and pyridine. Chapter 1 shows the influence that the saddle shape has on the self-assembling capabilities of this macrocycle when substituted with alkyl chains on the carbazoles. The restriction of the translational and rotational movements within a stack of carpyridines has resulted in two-dimensional supramolecular polymers in the form of sheets with micrometer lengths and molecular thicknesses in the absence of strong directional interactions. The elucidation of the composition of these nanosheets resulted in loosely packed columns driven by pi–pi interactions between monomers that associate laterally through Van der Waals interactions to form the two-dimensional surface. We term this process Shape-Assisted Self-Assembly. Chapter 2 contains the findings from further alkyl substitution on the para positions of the pyridines as a follow-up to Chapter 1. This results in tighter column formation and avoidance of lateral association between columns. A one-dimensional supramolecular polymer is then obtained, allowing for characterization of this new assembly both on surface and in solution. The self-assembly mechanism has been elucidated with different spectroscopic techniques, resulting in thermodynamic parameters comparable to those obtained from hydrogen-bonded systems. Chapter 3 entails the efforts in substituting one of the para positions of the pyridines with a hydrophilic sidechain, namely a triethyleneglycol. This affords an amphiphilic compound for which the self-assembly behavior can be studied in aqueous mixtures. Different morphologies like micelles or vesicles can be formed by the arrangement of the hydrophobic cores inside the supramolecular structure and the hydrophilic sidechains on the periphery in contact with water. Chapter 4 includes three different small projects that are related to the study of through- bond and through-space energy transfer within a carpyridine system. The first project seeks the synthesis of a carpyridine nanoring in which the electronic communication between monomers is enhanced by the presence of a metal ion inside the carpyridine cavity. This is favored due to the inherent curvature of the carpyridines and allows for guest complexation and study of energy transfer from the nanoring to the guest. The second project is based on a donor--acceptor approach by connecting the carpyridine to a donor and an acceptor moiety on each side of the pyridines. The presence or absence of a metal center will allow for studying energy transfer through bond or through space. Finally, the third project pursues the synthesis of a singlet fission relay in which one singlet fission chromophore will be connected to each side of the carpyridine. Analogously to the previous project, the metalation of the macrocycle will allow the study of singlet fission by energy transfer through bond or space.