Scaling Up Electronic Spin Qubits into a Three-Dimensional Metal–Organic Framework

Practical implementation of highly
coherent molecular spin qubits
for challenging technological applications, such as quantum information
processing or quantum sensing, requires precise organization of electronic
qubit molecular components into extended frameworks. Realization of
spatial control over qubit–qubit distances can be achieved
by coordination chemistry approaches through an appropriate choice
of the molecular building blocks. However, translating single qubit
molecular building units into extended arrays does not guarantee a
priori retention of long quantum coherence and spin–lattice
relaxation times due to the introduced modifications over qubit–qubit
reciprocal distances and molecular crystal lattice phonon structure.
In this work, we report the preparation of a three-dimensional (3D)
metal–organic framework (MOF) based on vanadyl qubits, [VO­(TCPP-Zn2-bpy)] (TCPP = tetracarboxylphenylporphyrinate; bpy = 4,4′-bipyridyl)
(1), and the investigation of how such structural modifications
influence qubits’ performances. This has been done through
a multitechnique approach where the structure and properties of a
representative molecular building block of formula [VO­(TPP)] (TPP
= tetraphenylporphyrinate) (2) have been compared with
those of the 3D MOF 1. Pulsed electron paramagnetic resonance
measurements on magnetically diluted samples in titanyl isostructural
analogues revealed that coherence times are retained almost unchanged
for 1 with respect to 2 up to room temperature,
while the temperature dependence of the spin–lattice relaxation
time revealed insights into the role of low-energy vibrations, detected
through terahertz spectroscopy, on the spin dynamics.