Title
Directing the self-assembly behaviour of porphyrin-based supramolecular systems
Author
Bert Meijer, Rob Weegen, Abraham Teunissen
Year
2017
Journal
Chemistry A European Journal
Abstract
The self-assembly behaviour of a library of tetra-amidated porphyrin molecules decorated with a variety of solubilizing wedges is investigated as dilute solutions in methylcyclohexane. Small changes in the solubilising wedge of the porphyrins resulted in different aggregated states, as evidenced by UV-Vis and CD spectroscopy. The porphyrins form either cofacially stacked H-aggregates or slip-stacked J-aggregates or a mixture of both. Detailed thermodynamic and kinetic analysis showed that in all cases the formation of J-aggregates proceeds via an isodesmic mechanism while H-aggregates are formed via a cooperative mechanism. It is shown that these aggregates assemble in a parallel pathway, in which both compete for the monomer, compared to a sequential pathway, in which one of the aggregates interconverts into the other. Interestingly, kinetic analysis of porphyrins that only form H-aggregates in thermodynamic equilibrium revealed that the competing pathway towards J-aggregates is operational in these systems as well. Our findings show that the balance between H- and J-aggregates depends on remarkably small changes in the architecture of the solubilising wedges.
Instrument
J-815
Keywords
Circular dichroism, Thermal stability, Aggregation, Biochemistry