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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
Infrared study of intercomponent interactions in a switchable hydrogen-bonded rotaxane
Dhiredj C Jagesar1, Frantisek Hartl, Wybren Jan Buma
1Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|December 8, 2007
Summary
Rotaxane molecular switches change structure when one electron is added, moving between binding sites. This conformational change is detected by observing shifts in infrared spectroscopy signals, showing how the macrocycle shields internal components from solvents.
Area of Science:
- Supramolecular Chemistry
- Molecular Machines
- Chemical Spectroscopy
Background:
- Rotaxanes are molecular machines with a macrocycle threaded onto a molecular axle.
- Hydrogen bonding plays a crucial role in the function and stability of rotaxane architectures.
- Controlling the position of the macrocycle on the axle is key to designing responsive molecular systems.
Purpose of the Study:
- To investigate the hydrogen bonding interactions within a specific rotaxane (rotaxane 1) in its neutral and reduced states.
- To analyze the influence of solvent polarity on these hydrogen bonding interactions and the rotaxane's conformation.
- To demonstrate the ability to controllably switch the rotaxane's structure using redox stimuli.
Main Methods:
- Infrared (IR) spectroscopy was employed to study hydrogen bonding between the macrocycle and binding stations.
- The study utilized various solvents to analyze solvent effects on vibrational frequencies.
- Correlations between vibrational frequencies and solvent acceptor number (AN) were examined.
Main Results:
- The macrocycle preferentially hydrogen bonds to the succinamide station in the neutral state.
- One-electron reduction of the naphthalimide station induces a conformational switch, moving the macrocycle.
- IR spectroscopy successfully detected these conformational changes via shifts in carbonyl (C=O) stretching frequencies.
- The macrocycle effectively shields the encapsulated station from solvent interactions, as evidenced by unaffected nu(CO) band wavenumbers.
Conclusions:
- Redox-induced conformational switching in rotaxanes can be precisely controlled and monitored using IR spectroscopy.
- Hydrogen bonding interactions are critical for dictating the preferred binding site of the macrocycle.
- The rotaxane architecture provides an intrinsic shielding effect for encapsulated guests against external solvent environments.
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