Hierarchical assembly is a generic motif of nature’s highly efficient photosynthetic systems: molecular sub-units (monomers) are assembled via weak, non-covalent interactions into individual supramolecular structures (supramolecular building blocks), which are then further assembled into close-packed superstructures. In nature, each level of hierarchy—from molecule, to supramolecular building block, to close-packed building blocks—plays an important role in the system’s intimate structure-function relationship. Gaining a detailed understanding of the fundamental self-assembly process is the pivotal next step for any future applications of supramolecular self-assembling. Though the forces behind self-assembly (e.g. hydrophobicity) are known, the specific mechanism by which monomers form the supramolecular structure still remains an open question. A crucial step towards formulating a complete mechanism is understanding the role of the monomer’s counter ion in the self-assembling process.<br/>I will discuss the complex correlation between the self-assembling conditions and the resulting structural properties by utilizing a well-defined artificial model system: supramolecular light-harvesting nanotubes (LHNTs) self-assembled in aqueous solution from cyanine dye molecules. Even though this system has been intensively studied, the details of the self-assembling process are still not understood. Due to hierarchical assembly, those LHNTs form bundled LHNTs with distinct spectroscopic signatures, which allows <i>in situ </i>real time monitoring of the self-assembling process via steady-state spectroscopy. In this study, counter ions with varying properties (e.g. polarizability) were employed to determine their role in the hierarchical assembling process of the LHNT. Specifically, I will discuss the impact of Na+, K+, Cs+, OH-, Cl-, I- that are studied as free ions (fully solvated cations and anions) and as paired ions (not fully solvated cations and anions). This study reveals how counterions with their specific cation and anion can be utilized to control the hierarchical self-assembling of supramolecular nanostructures. The results suggest that the non-participating components of the environment are as important to the self-assembling process as the components that directly participate in the self-assembling process. The results emphasize the high potential of environmental parameters for the engineering of supramolecular nanostructures.

Supramolecular self-assembly for light-harvesting: utilizing counterions for directing hierarchical assembling

254th National Meeting (2017)

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