Quantum Sensing of Electric Fields Using Spin-Correlated Radical Ion Pairs

摘要

Quantum sensing affords the possibility of using quantumentanglementto probe electromagnetic fields with exquisite sensitivity. In thiswork, we show that a photogenerated spin-correlated radical ion pair(SCRP) can be used to sense an electric field change created at oneradical ion of the pair using molecular recognition. The SCRP is generatedwithin a covalent donor-chromophore-acceptor systemPXX-PMI-NDI, 1, where PXX = peri-xanthenoxanthene, PMI = 1,6-bis(p-t-butylphenoxy)perylene-3,4-dicarboximide, and NDI = naphthalene-1,8:4,5-bis(dicarboximide).The electron-rich PXX donor in 1 acts as a guest moleculethat can be encapsulated selectively by a tetracationic cyclophaneExBox(4+) host to give a supramolecular complex 1 & SUB; ExBox ( 4+ ). Selectivephotoexcitation of the PMI chromophore results in ultrafast generationof the PXX & BULL;+-PMI-NDI & BULL;- SCRP. When PXX is encapsulated by ExBox(4+), the cyclophanegenerates an electric field that repels the positive charge on PXX & BULL;+ within PXX & BULL;+-PMI-NDI & BULL;-, reducing the SCRP distance, i.e., the distancebetween the centers-of-charge on the donor and acceptor. Pulse-EPRmeasurements are used to measure the coherent oscillations createdprimarily by the electron-electron dipolar coupling in theSCRP, which yields the distance between the two charges (spins) ofPXX(& BULL;+)-PMI-NDI & BULL;-. The experimental results show that the distance between PXX & BULL;+ and NDI & BULL;- decreases whenExBox(4+) encapsulates PXX & BULL;+, which demonstratesthat the SCRP can function as a quantum sensor to detect electricfield changes in the vicinity of the radical ions.