Ratiometric Luminescent Thermo‐Hygrometry, Metal‐Dependent Second Harmonic Generation, and Humidity‐Variable Magnetic Relaxation in a Manganese(II)‐Doped Zinc(II) Molecular Halide

ABSTRACT 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 (dppmO 2 ) 3 ][Zn II Cl 4 ]· n H 2 O ( 1 ) (dppmO 2 = bis(diphenylphosphino)methane) formula. The heterometallic {Zn II 0.9 Mn II 0.1 } material ( 2 ) exhibits dual photoluminescence (PL), including UV‐PL from dppmO 2 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 P na2 1 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.