Ratiometric Luminescent Thermo-Hygrometry, Metal-Dependent Second Harmonic Generation, and Humidity-Variable Magnetic...

Molecular materials based on metal complexes can link optical, electrical, and magnetic properties, all sensitive to external stimuli. This feature opens a pathway for their exploration as highly efficient sensors and advanced switches. We report the synthetic strategy for a truly multifunctional material linking dual-stimuli optical sensing with tunable nonlinear optical activity and chemically modulated magnetic response. This was realized by incorporating magneto-luminescent Mn(II) ions into a Zn(II) molecular halide of [Zn^II(dppmO₂)₃][Zn^IICl₄]·nH₂O (1) (dppmO₂ = bis(diphenylphosphino)methane) formula. The heterometallic {Zn^II _0.9Mn^II _0.1} material (2) exhibits dual photoluminescence (PL), including UV-PL from dppmO₂ ligands coordinated to Zn(II) and red-PL from d-d electronic transitions of octahedral Mn(II) centers. Thanks to this optical feature and water vapor sorption capability, 2 exhibits ratiometric luminescent thermo-hygrometry around the room-temperature (RT) region, being able to detect both temperature and relative humidity (RH) through the ratio between two PL signals. Due to the crystallization in the polar Pna2₁ space group, 1 and 2 exhibit distinct second-harmonic generation at RT, with its threefold enhancement induced by Mn(II) dopants. Thanks to the presence of Mn(II) complexes in the water-sensitive Zn(II) halide, 2 also reveals RH-variable slow relaxation of magnetization realized by modulation of a Raman process.