Sensing Chiral-Induced Spin Selectivity in Photogenerated Radical-Pairs with NV Centers via Lee-Goldburg Decoupling

Chiral-induced spin selectivity (CISS) refers to spin-dependent interactions between electrons and inversion asymmetric materials.¹ Recently, it has been hypothesized that the CISS effect could spin-polarize electrons during charge transfer in photoexcited donor-chiral bridge-acceptor (D-B-A) molecules which would have severe implications in biology as well as for quantum information science using spin qubit pairs.^2,3 However, whether charge transfer through the chiral bridge actually results in a spin-polarized state has not been resolved to date.⁴

 

We propose to exploit a near-surface nitrogen-vacancy (NV) center in diamond as a nanoscale, innocent sensor for spin polarization in radical pairs generated by D-B-A systems adsorbed on diamond surfaces.⁵ However, the pseudo-secular dipolar coupling which is essentially a spin flip-flop of the radical pair periodically interconverts the two polarized states. This would result in averaging of the initially generated spin polarization in sensing schemes where the dipolar coupling strength within the radical pair exceeds their coupling to the sensor spin.

 

Using spin dynamics simulations, we demonstrate that Lee-Goldburg decoupling, which is a common technique to mitigate homonuclear interactions in solid state NMR spectroscopy,⁶ can efficiently mitigate flip-flop processes in cases where the distance between the radical and NV greatly exceeds the radical pair separation. Besides avoiding signal averaging, we show that Lee-Goldburg decoupling can also act as a filter toward specific dipolar coupling strengths which allows to circumvent spatial averaging of couplings to multiple D-B-A molecules.