Hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1): A Dual Site Ligand That Supports Thermal Conformational Changes

A new
expanded porphyrin, hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1),
is reported. It was obtained via the condensation of a hexapyrrolic
derivative prepared in turn from a bipyrrole dialdehyde and a stable
quaterpyrrole precursor. This hexadecaphyrin contains eight direct
α-pyrrole-to-α-pyrrole linkages in its structure. It supports
the formation of bimetallic complexes of both zinc and cobalt that
are characterized by different conformational structures. Furthermore,
a mixed zinc/cobalt macrocycle has been prepared. The cobalt bimetallic
complex shows two stable conformations with the same oxidation state
that are in equilibrium. All compounds have been characterized by
common spectroscopic means, and single crystal X-ray diffraction structures
were obtained for all macrocyclic compounds. DFT calculations and
transient absorption spectra were used to study the electronic features
of the complexes and the effect of conformational changes. This system
shows promise as an accumulated heat sensor.