לוח שנה משולב

Most molecular self-assembly strategies involve equilibrium systems. Yet, strong noncovalent interactions may result in nonequilibrium self-assembly, where structural diversity is achieved by forming several kinetic products based on a single covalent building block. I demonstrate that well-defined amphiphilic molecular systems based on perylene diimide/peptide conjugates exhibit kinetically controlled self-assembly in aqueous medium, enabling pathway-dependent assembly sequences, in which different organic nanostructures are evolved in a stepwise manner. In order to better understand the processes leading to the ordered self-assembly of aromatic amphiphiles in water, a kinetic mechanistic study was performed. In this study, aqueous self-assembly of chiral perylene diimide (PDI) amphiphile into highly ordered crystalline arrays was investigated using UV-vis and circular dichroism (CD) spectroscopy coupled with cryogenic transmission electron microscopy (cryo-TEM). The latter provides direct structural imaging of self-assembly progress. Molecular dynamics calculations were performed as well. We observed a three-step mechanism: 1) nucleation; 2) growth; 3) coarsening. The nucleation-growth process fits a modified Kolmogorov /Johnson/Mehl/Avrami (KJMA) model. We observed that the initial state of the system is an amorphous aggregate that gradually transforms into a highly ordered system. Activation parameters suggest that de-solvation plays a significant role in the process.
Photophysical measurements of a set of materials similar to the ones studied in the kinetic part revealed excellent exciton mobility in ordered PDI arrays. The relation between structure and function was demonstrated using a set of kinetically formed structures that allow tuning of the exciton mobility via morphology of the self-assembled structures.