Chiral and racemic Dy(III) macrocyclic single-molecule magnets with magnetically enhanced photothermal conversion

We report a pair of enantiomeric complexes, Dy(R-L_N6)(mapp)₃·3H₂O (1R) and Dy(S-L_N6)(mapp)₃·3H₂O (1S), and their racemate, Dy(RS-L_N6)(mapp)₃·3H₂O, where R-/S-L_N6 and RS-L_N6 are macrocyclic ligands derived from the condensation of 2,6-pyridinedicarboxaldehyde with (1R,2R)/(1S,2S)-diaminocyclohexane, and Hmapp denotes methyl anthracen-9-ylphosphonate. Single-crystal structural analyses reveal that the Dy^III ions in 1R and 1RS possess similar coordination environments, and both complexes exhibit field-induced single-molecule magnet (SMM) behaviour with slight differences in the effective energy barriers. A significant difference is found in the intramolecular interactions between the axial mapp^- and equatorial macrocycle ligands. In 1R, two of the three anthracene groups are involved in π-π interactions with the equatorial pyridine rings, whereas in 1RS, all three anthracene rings participate in π-π interactions with the equatorial pyridine rings. Upon 395 nm illumination for 40 s, 1R and 1RS exhibit a similar temperature increase (ΔT = 65.6 for 1R and 66.8 °C for 1RS), but display distinct photothermal conversion efficiencies (η = 45.2% for 1R and 66.4% for 1RS), which can be enhanced by applying an external magnetic field (η = 54.8% for 1R and 75.3% for 1RS at 150 mT). This finding provides a new insight into the design of chiral functional molecular materials with multi-responsive properties.