Crystalline Small Molecule-Polymer Superlattice for Spatially Isolated Tetrathiafulvalene Spin Qubit Arrays

Molecular electron spins are compelling qubit candidates; however, mitigating their rapid relaxation and decoherence driven by structural disorder and phonon coupling remains a central challenge. Constructing molecular qubit frameworks (MQFs) represents a promising strategy to preserve quantum coherence by embedding spin centers in a rigid and ordered microenvironment. Here, we report a host-guest superlattice MQF by cocrystallizing tetrathiafulvalene (TTF) with a one-dimensional B←N coordination polymer (CityU-65). Encaging TTF radical spins within this highly ordered lattice establishes a rigid and magnetically dilute environment, effectively suppressing spin-lattice relaxation and partially mitigating spin decoherence. Consequently, CityU-65 preserves coherent spin addressability even under ambient conditions. At room temperature, the superlattice exhibits a prolonged spin-lattice relaxation time (T₁ = 9.6 µs) and a modestly improved phase-memory time (T_m = 0.9 µs) compared to pristine crystalline TTF. Our work establishes B←N superlattice cocrystallization as a powerful strategy for engineering designer quantum materials, providing a general guideline for the development of high-performance organic qubits through structural and phononic modulation.