TY - JOUR
T1 - Tuning the Supramolecular Chirality of One- and Two-Dimensional Aggregates with the Number of Stereogenic Centers in the Component Porphyrins
AU - Iavicoli, Patrizia
AU - Xu, Hong
AU - Feldborg, Lise Nørkjær
AU - Linares, Mathieu
AU - Paradinas, Markos
AU - Stafström, Sven
AU - Ocal, Carmen
AU - Nieto-Ortega, Belen
AU - Casado, Juan
AU - Navarrete, Juan T. López
AU - Lazzaroni, Roberto
AU - Feyter, Steven De
AU - Amabilino, David B.
PY - 2010
Y1 - 2010
N2 - A synthetic strategy was developed for the preparation of porphyrins containing between one
and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups
which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds reveal the
profound effects of this varying molecular chirality on their supramolecular structure and optical activity.
The number of stereogenic centers influences significantly the self-assembly and chiral structure of the
aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers
on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly
with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas
the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen
bonds induce the formation of an H-aggregate, and circular dichroism measurements and theoretical studies
indicate that the compounds self-assemble into helical structures. Both the chirality and stability of the
aggregates depend critically on the number of stereocenters. The chiral porphyrin derivatives gelate
methylcyclohexane at concentrations dependent on the number and position of chiral groups at the periphery
of the aromatic core, reflecting the different aggregation forces of the molecules in solution. Increasing the
number of stereogenic centers requires more material to immobilize the solvent, in all likelihood because
of the greater solubility of the porphyrins. The vibrational circular dichroism spectra of the gels show that
all compounds have a chiral environment around the amide bonds, confirming the helical model proposed
by calculations. The morphologies of the xerogels (studied by scanning electron microscopy and scanning
force microscopy) are similar, although more fibrous features are present in the molecules with fewer
stereogenic centers. Importantly, the presence of only one stereogenic center, bearing a methyl group as
the desymmetrizing ligand, in a molecule of considerable molecular weight is enough to induce singlehanded
chirality in both the one- and two-dimensional supramolecular self-assembled structures.
AB - A synthetic strategy was developed for the preparation of porphyrins containing between one
and four stereogenic centers, such that their molecular weights vary only as a result of methyl groups
which give the chiral forms. The low-dimensional nanoscale aggregates of these compounds reveal the
profound effects of this varying molecular chirality on their supramolecular structure and optical activity.
The number of stereogenic centers influences significantly the self-assembly and chiral structure of the
aggregates of porphyrin molecules described here. A scanning tunneling microscopy study of monolayers
on graphite shows that the degree of structural chirality with respect to the surface increases almost linearly
with the number of stereogenic centers, and only one handedness is formed in the monolayers, whereas
the achiral compound forms a mixture of mirror-image domains at the surface. In solution, four hydrogen
bonds induce the formation of an H-aggregate, and circular dichroism measurements and theoretical studies
indicate that the compounds self-assemble into helical structures. Both the chirality and stability of the
aggregates depend critically on the number of stereocenters. The chiral porphyrin derivatives gelate
methylcyclohexane at concentrations dependent on the number and position of chiral groups at the periphery
of the aromatic core, reflecting the different aggregation forces of the molecules in solution. Increasing the
number of stereogenic centers requires more material to immobilize the solvent, in all likelihood because
of the greater solubility of the porphyrins. The vibrational circular dichroism spectra of the gels show that
all compounds have a chiral environment around the amide bonds, confirming the helical model proposed
by calculations. The morphologies of the xerogels (studied by scanning electron microscopy and scanning
force microscopy) are similar, although more fibrous features are present in the molecules with fewer
stereogenic centers. Importantly, the presence of only one stereogenic center, bearing a methyl group as
the desymmetrizing ligand, in a molecule of considerable molecular weight is enough to induce singlehanded
chirality in both the one- and two-dimensional supramolecular self-assembled structures.
U2 - 10.1021/ja101533j
DO - 10.1021/ja101533j
M3 - Journal article
SN - 0002-7863
VL - 132
SP - 9350
EP - 9362
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
ER -