Abstract
Biradical spin probes can provide detailed information about the distances between molecules/regions of molecules because the through-space coupling of radical centres, characterised byJ, is strongly distance dependent. However, if the system can adopt multiple configurations, as is common in supramolecular complexes, the shape of the EPR spectrum is influenced not only byJbut also the rate of exchange between different states. In practice, it is often hard to separate these variables and as a result, the effect of the latter is sometimes overlooked. To demonstrate this challenge unequivocally we synthesised rotaxane biradicals containing nitronyl nitroxide units at the termini of their axles. The rotaxanes exchange between the available biradical conformations more slowly than the corresponding non-interlocked axles but, despite this, in some cases, the EPR spectra of the axle and rotaxane remain remarkably similar. Detailed analysis allowed us to demonstrate that the similar EPR spectral shapes result from different combinations ofJand rates of conformational interconversion, a phenomenon suggested theoretically more than 50 years ago. This work reinforces the idea that thorough analysis must be performed when interpreting the spectra of biradicals employed as spin probes in solution.
Original language | English |
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Pages (from-to) | 8385-8393 |
Number of pages | 9 |
Journal | Chemical Science |
Volume | 12 |
Issue number | 24 |
Early online date | 14 May 2021 |
DOIs | |
Publication status | Published - 28 Jun 2021 |
Bibliographical note
Funding Information:This research was supported by the Italian Ministry of University Research through the projects PRIN2017 “BacHounds: Supramolecular nanostructures for bacteria detection” (2017E44A9P to ML and EM) and “Nemo” (20173L7W8K to PF). SMG thanks the European Research Council (Consolidator Grant agreement 724987) for funding. SMG is a Royal Society Wolfson Research Fellow. We thank Lorenzo Sorace for helpful discussion.
Publisher Copyright:
© The Royal Society of Chemistry 2021.
ASJC Scopus subject areas
- General Chemistry