Unravelling Structural Dynamics, Supramolecular Behavior, and Chiroptical Properties of Enantiomerically Pure Macrocyclic Tertiary Ureas and Thioureas

The introduction of urea or thiourea functionality to
the macrocycle
skeleton represents an alternative way to control conformational dynamics
of chiral, polyamines of a figure-shaped periodical structure. Formally
highly symmetrical, these macrocycles may adapt diverse conformations,
depending on the nature of an amide linker and on a substitution pattern
within the aromatic units. The type of heteroatom X in the N–C­(X)–N
units present in each vertex of the macrocycle core constitutes the
main factor determining the chiroptical properties. In contrast to
the urea-containing derivatives, the electronic circular dichroism
of thioureas is controlled by the chiral neighborhood closest to the
chromophore. The dynamically induced exciton couplet is observed when
the biphenyl chromophores are present in the macrocycle core. In the
solid state, the seemingly disordered molecules may create ordered
networks stabilized by intermolecular S···halogen,
H···halogen, and S···H interactions.
The presence of two bromine substituents in each aromatic unit in
thiourea-derived trianglamine gives rise to a self-sorting phenomenon
in the crystal. In solution, this particular macrocycle exists as
a dynamic equimolar mixture of two conformational diastereoisomers,
differing in the spatial (clockwise and counter clockwise) arrangement
of the C–Br bonds. In the crystal lattice, macrocycles of a
given handedness assemble into homohelical layers.