Amplified Electron-Spin Thermal Sensitivity in Mn(II) Complexes

Abstract

Understanding the temperature sensitivity of magnetic resonance properties is an essential step toward any application of spin, whether for novel molecular thermometers or quantum sensing platforms. In that light, demonstrations that molecular tuning is effective at controlling the temperature dependence of the electron paramagnetic resonance spectra of open-shell molecules are vital. Herein we show that ligand choice offers one handle for controlling the temperature dependence of the EPR spectrum, ostensibly through modifying the temperature sensitivity of the zero-field splitting parameter, D. For this demonstration, we prepared and analyzed three different encapsulated Mn(II) complexes. High-field, high-frequency EPR spectroscopy reveal EPR spectra for all complexes that vary in width as a function of temperature. At lower temperatures, these temperature sensitivities change starkly with ligand shell, which yield 2.2 to 9.8 MHz/K thermal sensitivities for D.These results demonstrate the ability to modify the variable-T nature of D by ligand selection, the first such for the Mn(II) metal ion, and exhibit orders of magnitude enhancement over the nitrogen vacancy center of diamond (ca. 74 kHz/K).