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Issue 15, 2019
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Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor

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Abstract

Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor–bridge–acceptor (D–B–A) systems as well as competitive reaction pathways in acceptor–donor–acceptor (A–D–A) and acceptor–donor–acceptor′ (A–D–A′) systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV2+) and dipyridylthiazolothiazole (TTz2+) electron acceptors doubly-linked by means of two p-xylylene linkers (TTzExVBox4+), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox4+) to establish an A–D–A′ system, in which the ExV2+ and TTz2+ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz+˙–Per+˙–ExV2+ and TTz2+–Per+˙–ExV+˙ in <1 ps, while back electron transfer in TTz2+–Per+˙–ExV+˙ proceeds via the unusual sequence TTz2+–Per+˙–ExV+˙ → TTz+˙–Per+˙–ExV2+ → TTz2+–Per–ExV2+. In addition, selective chemical reduction of TTz2+ gives Per ⊂ TTzExVBox3+˙, turning the complex into a D–B–A system in which photoexcitation of TTz+˙ results in the reaction sequence 2*TTz+˙–Per–ExV2+ → TTz2+–Per–ExV+˙ → TTz+˙–Per–ExV2+. Both reactions TTz2+–Per+˙–ExV+˙ → TTz+˙–Per+˙–ExV2+ and TTz2+–Per–ExV+˙ → TTz+˙–Per–ExV2+ occur with a (16 ± 1 ps)−1 rate constant irrespective of whether the bridge molecule is Per+˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D–B–A systems.

Graphical abstract: Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor

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Publication details

The article was received on 10 Dec 2018, accepted on 06 Mar 2019 and first published on 11 Mar 2019


Article type: Edge Article
DOI: 10.1039/C8SC05514A
Chem. Sci., 2019,10, 4282-4292
  • Open access: Creative Commons BY license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor

    J. Zhou, Y. Wu, I. Roy, A. Samanta, J. F. Stoddart, R. M. Young and M. R. Wasielewski, Chem. Sci., 2019, 10, 4282
    DOI: 10.1039/C8SC05514A

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