ja5b08081_si_002.zip (102.81 kB)
Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds
dataset
posted on 2015-12-23, 00:00 authored by Cristina Oliveras-González, Florent Di Meo, Arántzazu González-Campo, David Beljonne, Patrick Norman, Maite Simón-Sorbed, Mathieu Linares, David B. AmabilinoA series of chiral synthetic compounds
is reported that shows intricate
but specific hierarchical assembly because of varying positions of
coordination and hydrogen bonds. The evolution of the aggregates (followed
by absorption spectroscopy and temperature-dependent circular dichroism
studies in solution) reveal the influence of the proportion of stereogenic
centers in the side groups connected to the chromophore ring in their
optical activity and the important role of pyridyl groups in the self-assembly
of these chiral macrocycles. The optical activity spans 2 orders of
magnitude depending on composition and constitution. Two of the aggregates
show very high optical activity even though the isolated chromophores
barely give a circular dichroism signal. Molecular modeling of the
aggregates, starting from the pyridine–zinc(II) porphyrin interaction
and working up, and calculation of the circular dichroism signal confirm
the origin of this optical activity as the chiral supramolecular organization
of the molecules. The aggregates show a broad absorption range, between
approximately 390 and 475 nm for the transitions associated with the
Soret region alone, that spans wavelengths far more than the isolated
chromophore. The supramolecular assemblies of the metalloporphyrins
in solution were deposited onto highly oriented pyrolitic graphite
in order to study their hierarchy in assembly by atomic force microscopy.
Zero and one-dimensional aggregates were observed, and a clear dependence
on deposition temperature was shown, indicating that the hierarchical
assembly took place largely in solution. Moreover, scanning electron
microscopy images of porphyrins and metalloporphyrins precipitated
under out-of-equilibrium conditions showed the dependence of the number
and position of chiral amide groups in the formation of a fibrillar
nanomaterial. The combination of coordination and hydrogen bonding
in the complicated assembly of these moleculeswhere there
is a clear hierarchy for zinc(II)-pyridyl interaction followed by
hydrogen-bonding between amide groups, and then van der Waals interactionspaves
the way for the preparation of molecular materials with multiple chromophore
environments.