Double Level Selection in a Constitutional Dynamic Library of Coordination Driven Supramolecular Polygons

A constitutional dynamic library
(CDL) of Cu­(II) metallo-supramolecular polygons has been studied as
a bench test to examine an interesting selection case based on molecular
recognition. Sorting of the CDL polygons is achieved through a proper
guest that is hosted into the triangular metallo-macrocycle constituent.
Two selection mechanisms are observed, a guest induced path and a
guest templated self-assembly (virtual library approach). Remarkably,
the triangular host can accommodate several guests with a degree of
selectivity ranging from ∼1 to ∼104 for all
possible guest pairs. A double level selection operates: guests drive
the CDL toward the triangular polygon, and, at the same time, this
is able to pick a specific guest from a set of competitive molecules,
according to a selectivity–affinity correlation. Association
constants of the host–guest systems have been determined. Guest
competition and exchange studies have been analyzed through variable
temperature UV–Vis absorption spectroscopy and single crystal
X-ray diffraction studies. Molecular structures and electronic properties
of the triangular polygon and of the host–guest systems also
have been studied by means of all electrons density functional theory
(DFT) and time-dependent density functional theory (TDDFT) calculations
including dispersive contributions. DFT outcomes ultimately indicate
the dispersive nature of the host–guest interactions, while
TDDFT results allow a thorough assignment of the host and host–guests
spectral features.