Effect of Electron-Nuclear Hyperfine Interactions on Multiple Quantum Coherences in Photogenerated Covalent Radical (Qubit) Pairs

Ultrafast photo-driven electron transfer reactions starting from an excited singlet state in an organic donor-acceptor molecule can generate a spin-correlated radical pair (RP) with an initially entangled spin state that may prove useful as a two-qubit pair in quantum information protocols. Here we investigate the effects of modulating electron-nuclear hyperfine coupling by rapidly transferring an electron between two equivalent sites comprising the reduced acceptor of the RP. A covalent electron donor-acceptor molecule including a tetrathiafulvalene (TTF) donor, a 4-aminonaphthalene-1,8-imide (ANI) chromophoric primary acceptor, and a m-xylene bridged cyclophane having two equivalent pyromellitimides (PI2), TTF-ANI-PI2, as a secondary acceptor was synthesized along with the analogous molecule having one pyromellitimide (PI) acceptor, TTF-ANI-PI. Photoexcitation of ANI within each molecule results in sub-nanosecond formation of TTF+•-ANI-PI-• and TTF+•-ANI-PI2-•. The effect of reducing electron-nuclear hy...