Magnetic fluorescent bifunctional spin-crossover complexes

Abstract

The rational design of magnetic and fluorescent bifunctional materials is attracting increasing interest. In this study, two mononuclear Fe(II) complexes, namely [Fe(L)₂(NCS)₂] (1) and [Fe(L)₂(NCSe)₂] (2) are synthesised by combining a spin-crossover unit and a fluorescent ligand (naphth-1-yl)-N-(3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)methanimine (L) to achieve bifunctionality. Single-crystal X-ray studies and magnetic measurements confirm the presence of spin crossover behaviours; these measurements agree with the results of the temperature depended Raman spectra and infrared spectra. Thermally and light-induced spin crossover is clearly observed for both complexes. The nature of the co-ligand (NCS⁻vs. NCSe⁻) shifts the transition temperature by approximately 60 K. The infrared spectra after irradiation reveal that the electronic states are ascribable to the photomagnetic effect at 10 K. Furthermore, temperature-dependent fluorescence emission spectra exhibit the coexistence of spin crossover and fluorescence for 1 and 2.