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Issue 38, 2018
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Reversible π-system switching of thiophene-fused thiahexaphyrins by solvent and oxidation/reduction

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Abstract

The concept of chemical topology has generated considerable interest among chemists and one of the state-of-the-art topics is Möbius topology in cyclic π-conjugated molecules. In this regard, expanded porphyrins have been extensively studied because of their facile topological interconversions and attractive optoelectronic properties. A typical example involves [28]hexaphyrins: they show topological conversion between planar Hückel and twisted Möbius topologies owing to their flexible structure. With this in mind, we designed a [28]hexaphyrin where one dimethine pyrrole unit was replaced with dithieno[3,4-b:3′,4′-d]thiophene (β-DTT), aiming at a reversible switching between macrocyclic and cross-conjugated π-systems by a change in molecular topologies. Considering that the β-DTT unit can offer both macrocyclic and cross-conjugated π-circuits, we envisioned that a combination of the topological interconversion of [28]hexaphyrin with the two π-circuits of the β-DTT unit would enable a reversible switching between macrocyclic and cross-conjugated π-circuits on Möbius and Hückel topologies, respectively, by a simple conformational change. Unexpectedly, the hexaphyrin revealed a unique, unprecedented π-system switching between a Möbius cross-conjugated π-system and a Hückel antiaromatic π-system, which was fully supported by both experimental and theoretical investigations. Meanwhile, the [28]hexaphyrin was also found to be redox interconvertible with the corresponding [26]hexaphyrin with a Hückel cross-conjugated π-system. These results demonstrate that the β-DTT unit is a new effective motif to realize π-system switching by changing molecular and π-system topologies. Importantly, external stimuli, i.e., solvent, as well as oxidation/reduction can be used to trigger the topological changes in expanded porphyrins with the help of the β-DTT unit.

Graphical abstract: Reversible π-system switching of thiophene-fused thiahexaphyrins by solvent and oxidation/reduction

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Supplementary files

Article information


Submitted
04 Jun 2018
Accepted
07 Aug 2018
First published
14 Aug 2018

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2018,9, 7528-7539
Article type
Edge Article

Reversible π-system switching of thiophene-fused thiahexaphyrins by solvent and oxidation/reduction

T. Higashino, A. Kumagai, S. Sakaki and H. Imahori, Chem. Sci., 2018, 9, 7528
DOI: 10.1039/C8SC02448K

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