Donor-acceptor functionalized coordination cages for photoinduced charge separation

Coordination cages are nanoscale objects that self-assemble from organic ligands and metal ions. Owing to their accessible cavities, they serve as hosts for binding, stabilizing, or converting guest molecules. Moreover, they can be utilized as scaffolds for arranging different functionalities in space. This dissertation advances the rational design approaches for assemblies PdnL2n, composed of Pd(II) ions and bis-pyridyl ligands L, of a particular structure and function. In the first part of the thesis, a relationship between the nuclearity of coordination rings PdnL2n and the binding angle of the constituent organic ligand was sketched. For this, the self-assembly of stiff bis-pyridyl ligands of varying geometries was investigated. Intriguingly, the formation of the first non-templated homoleptic Pd5L10 ring was observed when the ligand angle was adjusted to 84°. The results were supported by DFT computations as well as models based on geometrical considerations. The shape complementary assembly (SCA) approach was applied for synthesizing a library of donor-acceptor functionalized cages cis-Pd2D2A2 to achieve photoinduced charge separation. Importantly, donor and acceptor moieties are arranged at defined distances within the cages. This allows their usage as a modular platform for deriving structure-function relationships. Here, the dependency of the rate constant of charge recombination on the thermodynamic driving force of the same process was studied. The cages’ structural, photophysical, and electrochemical properties were thoroughly investigated. Correlation of the thermodynamic and kinetic data for the dominating charge recombination process indicates Marcus inverted region behavior, meaning that an increase in the exergonicity is accompanied by a decrease in the rate constant. Aiming at vectorial electron transfer, first steps towards the formation of vesicular materials based on donor-acceptor cages were undertaken. Functionalization of the donor ligand of one of the cis-Pd2D2A2 cages with nonpolar alkyl chains endowed the cage with amphiphilicity. Preliminary results indicate that the cages assemble into agglomerates with a diameter of around 100 nm in the tested polar organic solvents.