Tunable Charge Transport\nand Spin Dynamics in Two-Dimensional\nConjugated Metal–Organic Frameworks

Abstract

Two-dimensional conjugated metal–organic frameworks\n(2D\nc-MOFs) have attracted increasing interest in electronics due to their\n(semi)­conducting properties. Charge-neutral 2D c-MOFs also possess\npersistent organic radicals that can be viewed as spin-concentrated\narrays, affording new opportunities for spintronics. However, the\nstrong π-interaction between neighboring layers of layer-stacked\n2D c-MOFs annihilates active spin centers and significantly accelerates\nspin relaxation, severely limiting their potential as spin qubits.\nHerein, we report the precise tuning of the charge transport and spin\ndynamics in 2D c-MOFs via the control of interlayer stacking. The\nintroduction of bulky side groups on the conjugated ligands enables\na significant dislocation of the 2D c-MOFs layers from serrated stacking\nto staggered stacking, thereby spatially weakening the interlayer\ninteractions. As a consequence, the electrical conductivity of 2D\nc-MOFs decreases by 6 orders of magnitude, while the spin density\nachieves more than a 30-fold increase and the spin–lattice\nrelaxation time (<i>T</i>₁) is increased up to\n∼60 μs, hence being superior to the reference 2D c-MOFs\nwith compact stackings whose spin relaxation is too fast to be detected.\nSpin dynamics results also reveal that spinless polaron pairs or bipolarons\nplay critical roles in the charge transport of these 2D c-MOFs. Our\nstrategy provides a bottom-up approach for enlarging spin dynamics\nin 2D c-MOFs, opening up pathways for developing MOF-based spintronics.