Synthetic Approach To Determine the Effect of Nuclear Spin Distance on Electronic Spin Decoherence

Nuclear–electronic
interactions are a fundamental phenomenon
which impacts fields from magnetic resonance imaging to quantum information
processing (QIP). The realization of QIP would transform diverse areas
of research including accurate simulation of quantum dynamics and
cryptography. One promising candidate for the smallest unit of QIP,
a qubit, is electronic spin. Electronic spins in molecules offer significant
advantages with regard to QIP, and for the emerging field of quantum
sensing. Yet relative to other qubit candidates, they possess shorter
superposition lifetimes, known as coherence times or T2, due to interactions with nuclear spins in the local
environment. Designing complexes with sufficiently long values of T2 requires an understanding of precisely how
the position of nuclear spins relative to the electronic spin center
affects decoherence. Herein, we report the first synthetic study of
the relationship between nuclear spin–electron spin distance
and decoherence. Through the synthesis of four vanadyl complexes,
(Ph4P)2[VO­(C3H6S2)2] (1), (Ph4P)2[VO­(C5H6S4)2] (2),
(Ph4P)2[VO­(C7H6S6)2] (3), and (Ph4P)2[VO­(C9H6S8)2] (4), we are able to synthetically place a spin-laden propyl
moiety at well-defined distances from an electronic spin center by
employing a spin-free carbon–sulfur scaffold. We interrogate
this series of molecules with pulsed electron paramagnetic resonance
(EPR) spectroscopy to determine their coherence times. Our studies
demonstrate a sharp jump in T2 when the
average V–H distance is decreased from 6.6(6) to 4.0(4) Å,
indicating that spin-active nuclei sufficiently close to the electronic
spin center do not contribute to decoherence. These results illustrate
the power of synthetic chemistry in elucidating the fundamental mechanisms
underlying electronic polarization transfer and provide vital principles
for the rational design of long-coherence electronic qubits.