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

Abstract

Here, we use a pyridinecarbaldehyde rhodamine 6G hydrazone ligand (L) to synthesize an Fe­(II) complex <b>1</b> 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 <b>1</b> show that three-step SCO takes place in the temperature range of 120–350 K, and its desolvated form <b>1-d</b> exhibits SCO around room temperature (<i>T</i>_c↑ = 343 K and <i>T</i>_c↓ = 303 K) with a wide hysteresis loop of 40 K. Moreover, complex <b>1-d</b> displays light-induced excited spin-state trapping phenomenon. Intriguingly, the fluorescence intensity of the maximum emission at 560 nm for complex <b>1-d</b> displays discontinuous variation in the range of 250–400 K, indicative of the occurrence of synergetic fluorescence and SCO