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Controllable donor-acceptor neutral [2]rotaxanes.

Takahiro Iijima1, Scott A Vignon, Hsian-Rong Tseng

  • 1California NanoSystems Institute, Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569, USA.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|November 9, 2004
PubMed
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This study synthesized novel bistable [2]rotaxanes, demonstrating controllable movement of a crown ether ring between electron-accepting units. Lithium ions were shown to effectively switch the rotaxane

Area of Science:

  • Supramolecular Chemistry
  • Molecular Machines
  • Organic Synthesis

Background:

  • Bistable [2]rotaxanes are molecular systems capable of existing in two distinct states.
  • Controlling the movement of molecular components is crucial for developing advanced molecular machines.
  • Crown ethers and diimide units are key components in supramolecular chemistry for molecular recognition and electron transfer.

Purpose of the Study:

  • To synthesize neutral bistable [2]rotaxanes with tetraarylmethane stoppers and a 1,5-dinaphtho[38]crown-10 (1/5DNP38C10) ring.
  • To investigate the slippage and shuttling behavior of the 1/5DNP38C10 ring between pyromellitic diimide (PmI) and 1,4,5,8-naphthalenetetracarboxylate diimide (NpI) units.
  • To explore the influence of Li+ ions on the rotaxane's structure and function.

Main Methods:

Related Experiment Videos

  • Modular synthesis of dumbbell-shaped compounds (NpPmD, PmPmD, NpNpD).
  • Preparation of bistable [2]rotaxanes (NpPmR, PmPmR, NpNpR) via slippage.
  • Dynamic 1H NMR spectroscopy to study molecular movement and activation barriers.
  • Photophysical and electrochemical property investigations.
  • Li+ ion titration experiments.

Main Results:

  • The 1/5DNP38C10 ring shuttles between PmI and NpI units, with higher activation barriers for NpI, indicating stronger donor-acceptor interactions.
  • Charge-transfer bands were observed, correlating with the electron-accepting strengths of PmI and NpI.
  • In NpPmR, the 1/5DNP38C10 ring preferentially encircles the NpI unit, confirmed by reduction potentials.
  • One-electron reduction of NpI causes the 1/5DNP38C10 ring to move to the PmI unit.
  • Li+ ions significantly strengthen donor-acceptor interactions, promoting the movement of 1/5DNP38C10 from NpI to PmI.

Conclusions:

  • The synthesized [2]rotaxanes exhibit controllable bistability and molecular shuttling behavior.
  • The strength of donor-acceptor interactions dictates the preferred position of the crown ether ring.
  • Li+ ions act as external stimuli to controllably switch the rotaxane's state, demonstrating potential for molecular switches.
  • The reversibility of Li+-ion-induced switching was demonstrated using [12]crown-4.