Influencing reactions with directed electric field has been a long endeavor for chemists. Besides application of an external field from a macroscopic electrode, another approach can be placing ions at well-defined locations from the target reactive site. In this work we have created a crown-ether with a benzonitrile Stark shift probe. This crown ether can capture a variety of +1, +2 and +3 cations and the electric field created by these trapped metal ions can be quantified from the frequency shift of the probe. We demonstrate that the Stark probe frequency blue-shifts in most of the cases and this blue-shift increases with the charge of the metal ion, as expected. Along with the Stark-shift of the nitrile probe, we have observed another broad peak which is ~30-40 cm<sup>-1</sup> blue-shifted from the ion-free crown ether nitrile peak. This arises due to specific Lewis bonding between the lone-pair of nitrile and the free metal ions present in the solvent. Our model molecule is capable of distinguishing two types of influences on the nitrile frequency and therefore can help resolve the interpretational ambiguities in vibrational Stark shift studies. This work will also help guide molecular design principles for engineering tailored electric fields at the microscopic scale.

Distinguishing between Lewis interaction and electrostatic interaction using a crown ether functionalized stark probe

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ACS Fall 2022

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