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 H L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M L (py) ] (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 [Cu Ni L (py) ] (5), [Co Ni L (py) ] (6), [Co Cu L (py) ] (7), [Cu Zn L (py) ] (8), and [Ni Zn L (py) ] (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 (T =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.

The Second Quantum Revolution: Role and Challenges of Molecular Chemistry

“…A switchable interaction between two target-qubits might be alternatively achieved by exploiting the properties of a complex that undergoes spin-crossover transition or redox isomerism 83,84 upon application of an external stimulus (temperature, light, magnetic or electric fields) or by the insertion of a photoactive spacer. 85 Although to date these methods have not been deeply examined, an efficient and fast enough switching of the interaction between qubits is needed to be exploited in real applications. Under this respect, photogeneration of spin triplets states from radical ligands 86 or radical pairs from diamagnetic ligands 87 can be regarded as one of the few viable ways to achieve fast exchange switching between qubits.…”

A perspective on scaling up quantum computation with molecular spins

“…49 proposals for introducing switchable couplers within molecular or supramolecular structures, formed by either ancillary spin qubits 58 or by molecular linkers that can modify its electronic structure under some external stimulus. 66 Yet, at some point, this path must be complemented with the ability to locally control and, specifically, wire up in a tunable manner different individual molecular spins.…”

Metal complexes bearing photochromic ligands: photocontrol of functions and processes

“…At the end of this section, we would like to point out the innovative approach of Aromi et al to provide DTE-light switchable qubits systems where the magnetic interaction between weakly coupled spins with long quantum coherence can be switched on and off with light. 73,74 These systems are of interest for quantum computing realizations.…”