Molecules designed to contain two weakly coupled spins with a photoswitchable spacer

Abstract

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=urn:x-wiley:09476539:media:chem201702171:chem201702171-math-0001 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.