Joris van Slageren, Simon J. Teat, Marta Estrader, Olivier Roubeau, Jorge Salinas Uber, Guillem Aromí, Anna Sadurní, Nicholas F. Chilton, Paul Lloyd-Williams, Jordi Ribas-Ariño, Jordi Garcia, Dominik Dengler
Controlling the charges and spins of molecules lies at the heart of spintronics. A photoswitchable molecule consisting of two independent spins separated by a photoswitchable moiety was designed in the form of new ligand H4L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M4L2(py)6] (M=Cu, 1; Co, 2; Ni, 3; Zn, 4) were prepared and studied by single-crystal X-ray diffraction (SCXRD). Different metal centers can be selectively distributed among the two chemically distinct sites of the ligand, and this enables the preparation of many double-spin systems. Heterometallic [MM′⋅⋅⋅M′M] analogues with formulas [Cu2Ni2L2(py)6] (5), [Co2Ni2L2(py)6] (6), [Co2Cu2L2(py)6] (7), [Cu2Zn2L2(py)6] (8), and [Ni2Zn2L2(py)6] (9) were prepared and analyzed by SCXRD. Their composition was established unambiguously. All complexes exhibit two weakly interacting [MM′] moieties, some of which embody two-level quantum systems. Compounds 5 and 8 each exhibit a pair of weakly coupled S=1/2
spins that show quantum coherence in pulsed Q-band EPR spectroscopy, as required for quantum computing, with good phase memory times (TM=3.59 and 6.03 μs at 7 K). Reversible photoswitching of all the molecules was confirmed in solution. DFT calculations on 5 indicate that the interaction between the two spins of the molecule can be switched on and off on photocyclization.
Spin control: Tetranuclear coordination complexes with predetermined homometallic [MM⋅⋅⋅MM] or heterometallic [MM′⋅⋅⋅MM′] topology (M, M′=Cu, Co, Ni, Zn) and photoswitchable spacers were synthesized as potential models of spin-based two-qubit quantum gates. All the heterometallic complexes exhibit two well-defined, weakly interacting magnetic entities. The resonance between two magnetic levels of these units could be used for implementation of a qubit. The reversible cyclization triggered by photoswitching turns the interaction between the two spins of the molecule on and off.
