A photochromic trinuclear dysprosium(iii) single-molecule magnet with two distinct relaxation processes

Abstract

Multifunctional molecules responsive to light are highly desired as components for the construction of remotely controlled nanodevices. Here we present a Dy^III single molecule magnet (SMM) comprising dithienylethene (dte) photochromic bridging ligands in the form of a pyridine (py) derivative: 1,2-bis((2-methyl-5-pyridyl)thie-3-yl)perfluorocyclo-pentene (dtepy). The title trinuclear compound {[Dy^III(BHT)₃]₃(dtepy)₂}·4C₅H₁₂ (1) was synthesized by combining the low-coordinate dysprosium complexes Dy^III(BHT)₃ (BHT = 2,6-di-tert-butyl-4-methylphenolate) with dtepy bridging ligands in the ‘open’ form using n-pentane as a completely inert solvent. The trinuclear molecule comprises two different Dy^III centers due to its quasi-linear geometry: a central trigonal bipyramidal Dy^III ion and two peripheral ones with an approximate trigonal pyramidal geometry. Thanks to that, 1 shows two types of SMM behavior which is slightly affected by the photoisomerization of the photochromic dtepy bridges. The impact of the photoisomerization on the magnetization dynamics was studied by means of alternating current (AC) magnetic susceptibility measurements for the ‘open’ and ‘closed’ forms of the molecules. The changes between the ‘open’ and ‘closed’ isomers were further investigated by IR and UV-vis spectroscopy, suggesting the co-existence of the ligand-related photochromism and single-molecule magnet behavior in 1. However, the powder X-ray diffraction studies indicate loss of structural order in the first photoisomerization step preventing in-depth studies.