Construction of Magneto-Fluorescent Bifunctional Spin-Crossover Fe(II) Complex from Pyrene-Decorated Pybox Ligand

Graphical A magneto-fluorescent bifunctional Fe(II) complex is synthesized through decoration of the pyrene fluorophore to Fe(II)-pybox moiety. Its magnetic and fluorescent properties are characterized via X-ray structural analyses, magnetic susceptibility measurement, 57 Fe Mössbauer spectroscopy, and fluorescent spectroscopy. As expected, the coexistence of spin-crossover and fluorescence is achieved. The construction of magneto-fluorescent bifunctional complexes is a feasible approach toward multifunctional molecular materials. Herein we report the synthesis and properties studies of a mononuclear Fe(II) complex [Fe L 2 ](ClO 4 ) ( 1 ), where L is a pyridine-2,6-bis(oxazoline) (pybox) ligand decorated by the pyrene fluorophore. Magnetic susceptibility measurement of desolvated complex 1-d shows an incomplete and gradual spin-crossover in the temperature range 50–300 K, which is further confirmed via 57 Fe Mössbauer spectroscopy study. Light-induced excited spin state trapping (LIESST) is also observed below 70 K when the powder sample is irradiated by a 532 nm laser. The change in absorption during the spin-crossover (SCO) process is investigated via the temperature-dependent UV-vis spectroscopy. As expected, through introducing the chromophore, 1 displays fluorescence in both solution and solid state, achieving the coexistence of spin-crossover and fluorescence in one compound.