Self-assembly of oligomeric dipyrromethene metal complexes

The study of metallosupramolecular complexes has become an active research field in recent years. These complexes are formed through self-assembly processes driven by ligand-metal coordination, and they are widely used in molecular electronic, catalyst, host-guest chemistry and gas storage applications. Dipyrromethenes (dipyrrins) can act as monoanionic ligands which coordinate with various metals to form charge-neutral metal complexes. In the past decade, α,α’-linked and β,β’-linked bis(dipyrromethene)s have drawn considerable attention as building blocks for various supramolecular architectures. Surprisingly, limited work has been done to study meso-substituted dipyrrinato metal complexes. The primary objective of this project was to investigate meso-substituted dipyrrinato complexes and to synthesize novel meso-bridged bis(dipyrromethene) ligands to explore their capabilities for use in supramolecular systems. A new type of ligand which incorporates both boron-linked dipyrromethenes and free-base dipyrromethenes was synthesized and treated with various metals to form complexes. These metal complexes exhibit different structural features depending on the central metal or substituents on the dipyrromethenes, and the correlations between the structural features and optical properties were established. Also, a one-side BF₂-protected bis(dipyrromethene) ligand was used for stepwise oligomerization to form extended dipyrromethene arrays. Different methods to achieve these linear dipyrrin arrays were explored. Heteroleptic metal dipyrrin complexes can act as both the ligand and metal ion source to coordinate with free-base dipyrrin ligands, leading to the formation of oligomeric linear complexes incorporating the same or different metals. Further, differently angled spacers were employed to link two dipyrrin moieties at the meso-position. Depending on the angle of the spacer, the coordination reactions between bis(dipyrromethene)s and metals produced self-assembled cyclic oligomers with different core sizes. When the two dipyrrin moieties were oriented 86˚ apart, the resulting products ranged from trimer to hexamer. The trimeric and pentameric structures were determined by X-ray diffraction analysis, and the macrocycles display channel structures formed through intermolecular π-π or CH/π interactions. In contrast, when the two dipyrrin moieties were 35˚ apart, the main product was the dimer with trace amounts of tetramer. Finally, the coordination between linear heteroleptic metal dipyrrin complexes and the 35˚ angled bis(dipyrromethene) ligand produced a mixed-ligand complex.Science, Faculty ofChemistry, Department ofGraduat