Rhodamine 6G-Labeled Pyridyl Aroylhydrazone Fe(II) Complex Exhibiting Synergetic Spin Crossover and Fluorescence

Here,
we use a pyridinecarbaldehyde rhodamine 6G hydrazone ligand
(L) to synthesize an Fe­(II) complex 1 for the search
of new fluorescent-spin crossover (SCO) materials. Single-crystal
structural determinations suggest that the Fe­(II) ion is chelated
by two ring-opened ligands (L-o) to form a FeN4O2 coordination environment, and intermolecular π---π contacts
of the xanthene groups connect the adjacent molecules to form a supramolecular
one-dimensional chain. Magnetic susceptibility measurements on complex 1 show that three-step SCO takes place in the temperature
range of 120–350 K, and its desolvated form 1-d exhibits SCO around room temperature (Tc↑ = 343 K and Tc↓ = 303
K) with a wide hysteresis loop of 40 K. Moreover, complex 1-d displays light-induced excited spin-state trapping phenomenon. Intriguingly,
the fluorescence intensity of the maximum emission at 560 nm for complex 1-d displays discontinuous variation in the range of 250–400
K, indicative of the occurrence of synergetic fluorescence and SCO.