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.

本研究报道了一种新型扩环卟啉——十六卟啉-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1)（hexadecaphyrin-(1.0.0.0.1.1.0.1.1.0.0.0.1.1.0.1)）。该化合物由六吡咯衍生物经缩合反应制得，而该六吡咯衍生物则依次由联吡咯二醛与稳定的四吡咯前驱体合成。其分子结构中包含八个直接的α-吡咯至α-吡咯连接键。该十六卟啉可形成锌与钴的双金属配合物，且这些配合物具有不同的构象结构。此外，本研究还制备了锌/钴混合金属大环化合物。钴双金属配合物存在两种具有相同氧化态的稳定构象，二者处于动态平衡之中。所有化合物均通过常规光谱手段完成表征，所有大环化合物的单晶X射线衍射（single crystal X-ray diffraction）结构均已解析获得。本研究借助密度泛函理论（DFT, Density Functional Theory）计算与瞬态吸收光谱，探究了配合物的电子特性以及构象变化所产生的影响。该体系作为累积热传感器具有良好的应用潜力。