MPS/CHE-EPSRC: Synthetic Molecular Compasses

With support from the Division of Chemistry, Professors Michael R. Wasielewski and Matthew D. Krzyaniak of Northwestern University, along with their collaborators at the University of Oxford in the United Kingdom, are developing molecular compasses capable of sensitive detection of both the magnitude and direction of weak magnetic fields with applications in quantum sensing and quantum navigation. Many animals, including night-migratory songbirds, navigate using the Earth's magnetic field. Although the mechanisms are not fully understood, mounting evidence points to Nature employing coherently driven quantum processes to detect magnetic interactions a million times weaker than the thermal energy in biological tissue. According to this hypothesis, blue light photoexcitation of cryptochrome, a protein in the retinas of the animals' eyes, generates short-lived radicals whose reaction yields and rates are sensitive to the direction and strength of ambient magnetic fields. This project will generate fundamental insights into the quantum dynamics of these magneto-receptors and exploit that understanding by synthesizing and characterizing ultrasensitive molecular compasses. In addition, this project will provide the advanced education for students necessary for developing a quantum workforce. This award is made under the NSF-UKRI lead agency opportunity. This project will use a collaborative approach to prepare a family of bespoke, high sensitivity chemical compasses. It will combine synergistically the power of chemical synthesis, which offers broad flexibility in molecular design, with a suite of state-of-the-art spectroscopies and powerful quantum mechanical simulation techniques to explore the compasses' spin dynamics and refine their sensitivity to weak magnetic fields. The magnetic field response of two types of photo-generated spin-correlated pairs will be investigated: (a) doublet pairs in molecular electron donor-bridge-acceptor (D-B-A) triads, and (b) triplet pairs produced by singlet fission in polyacene single crystals. In both systems, the sensitivity of the compasses to magnetic fields will be enhanced by optimizing their molecular structures through chemical synthesis and crystal engineering. In parallel, their molecular structure-property relationships will be elucidated through theoretical simulations. All systems will be characterized using a combination of sensitive optical techniques, magnetometry, and electron spin resonance spectroscopy. Photoluminescence from triplet states generated by singlet fission in the polyacenes and radical ion pair recombination within D-B-A triads will serve as an optical read-out to enhance magnetic field detection sensitivity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.