Harnessing ligand design to develop primary and self-calibrated luminescent thermometers with field-induced single ion magnet behaviour in Dy3+ complexes

abstract

Novel complexes {[Dy(L-N6en)(OAc)(2)](NO3)}2H(2)O (12H(2)O) and {[Dy(L-N6prop)(OAc)(2)](NO3)}CHCl3 (2CHCl3), containing partially flexible symmetric N-6 macrocycles, are reported. We explore the influence of the spacer length between two symmetrical N-3 rigid moieties of the ligand on their structural, magnetic, and luminescence properties. Crystallographic analysis reveals the presence of Dy3+ ions in distorted tetradecahedral (12H(2)O) or bicapped square antiprism (2CHCl3) environments. This underscores the increased flexibility of the L-N6prop ligand, resulting in greater distortion of the N-6 macrocycle plane. Both complexes exhibit single-molecule magnet behaviour under an optimal field of 2000 Oe, with 2CHCl3 displaying the highest U-eff value of 127 K, despite its less planar N-6 macrocycle. Luminescence measurements indicate that the ratio between the integrated intensity of the ligands and that of the the Dy3+ 4F9/2 -> H-6(13/2) transition can define secondary luminescent thermometers. Maximum relative thermal sensitivity values of 2.3 (12H(2)O) and 5.1% K-1 (2CHCl3) are achieved. Furthermore, deconvolution of the F-4(9/2) -> H-6(15/2) transition in 2CHCl3 supports the previous determination of the energy barrier for magnetic relaxation. This permits the demonstration of the first example of a Dy3+ primary luminescent thermometer based on two thermally coupled Kramer's doublets of the F-4(9/2) level. Remarkably, 2CHCl3 is also the first self-calibrated luminescent thermometer with magnetic relaxation operating within the 86-211 K range, showcasing its potential in precise temperature sensing applications.

keywords

MOLECULE MAGNETS; SLOW RELAXATION; MAGNETIZATION; ZN2DY

subject category

Chemistry

authors

Corredoira-Vazquez, J; Gonzalez-Barreira, C; Garcia-Deibe, AM; Sanmartin-Matalobos, J; Hernandez-Rodriguez, MA; Brites, CDS; Carlos, LD; Fondo, M

our authors

acknowledgements

This work was developed within the scope of the project CICECO - Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020, financed by national funds through the FCT/MCTES (PIDDAC). This article is also based upon work from COST Action CA22131, supported by COST (European Cooperation in Science and Technology). The authors acknowledge fruitful discussions with Dr Albano N. Carneiro Neto (University of Aveiro) concerning ligand-to-metal energy transfer. J. C. V. also thanks Xunta de Galicia for his postdoctoral fellowship (ED481B-2022-068).

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