Direct detection of spin polarization in photoinduced charge transfer through a chiral bridge

TL;DR

This paper demonstrates that time-resolved EPR spectroscopy can directly detect long-lived spin polarization caused by photoinduced charge transfer through a chiral bridge, advancing understanding of spin selectivity in chiral systems.

Contribution

It provides the first direct proof of spin polarization detection via EPR in a chiral charge transfer system, with theoretical modeling supporting chirality-induced spin selectivity.

Findings

Time-resolved EPR detects spin polarization in a CdSe QD-C60 system.

Charge transfer results in a long-lived C60 radical anion with spin polarization.

Theoretical spectra suggest compatibility with chirality-induced spin selectivity.

Abstract

It is well assessed that the charge transport through a chiral potential barrier can result in spin-polarized charges. The possibility of driving this process through visible photons holds tremendous potential for several aspects of quantum information science, e.g., the optical control and readout of qubits. In this context, the direct observation of this phenomenon via spin-sensitive spectroscopies is of utmost importance to establish future guidelines to control photo-driven spin selectivity in chiral structures. Here, we provide direct proof that time-resolved electron paramagnetic resonance (EPR) can be used to detect long-lived spin polarization generated by photoinduced charge transfer through a chiral bridge. We propose a system comprising CdSe QDs, as a donor, and C60, as an acceptor, covalently linked through a saturated oligopeptide helical bridge (\c{hi}) with a rigid structure of ~ 10{\AA}. Time-resolved EPR spectroscopy shows that the charge transfer in our system results in a C60 radical anion, whose spin polarization maximum is observed at longer times with respect to that of the photogenerated C60 triplet state. Notably, the theoretical modeling of the EPR spectra reveals that the observed features may be compatible with chirality-induced spin selectivity and identifies which parameters need optimization for unambiguous detection of the phenomenon. This work lays the basis for the optical generation and direct manipulation of spin polarization induced by chirality.