Conjugated Porphyrin Tapes as Quantum Mediators for Vanadyl Qubits

Vanadium(IV) magnetic centers are prime candidates as molecular quantum information units. One of the longstanding problems is to obtain an extendable scaffold that transmits the magnetic interaction to a degree usable for quantum processing, and allows upscaling to multiple centers, while preserving a sufficiently long coherence time. Here, we show that fused porphyrins allow tailored scaffolding of vanadyl quantum units, with an almost flat conjugated π-system that offers substantial advantages for communication between vanadyl ions, leading to the long spin-lattice (T1 = 30 ms) and coherence (Tm = 5.5 µs) times. The antiferromagnetic exchange coupling in these vanadyl dimers (J = 1 GHz) is stronger than the hyperfine interaction, resulting in complex EPR spectra in which both unpaired electrons couple equally to both I = 7/2 51V nuclei. Isolation of the syn- and anti-isomers, with vanadyls on the same or opposite sides of the con-jugated channel, showcases the sensitivity of quantum units to different configurational environments, and offers a way to tune the inter-action in poly-porphyrin systems by controlling the stereochemistry.