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 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 FeNO 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 ( T↑ = 343 K and T↓ = 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.

A Two‐Dimensional Iron(II) Coordination Polymer with Synergetic Spin‐Crossover and Luminescent Properties

“…The design and synthesis of multifunctional materials, especially those featuring an interplay or synergy between two or more properties,have attracted considerable attention in recent years. [1] Theintrinsic properties of the building units commonly used include luminescence, [2] magnetism, [3] electrical conductivity, [4] and chirality. [5] Among them, ahighlight area is the combination of spin crossover (SCO) and luminescence,w hich may expand the horizon of SCO-based applications,e specially in magneto-optical switches.T he optical properties of the Fe II core have been well-documented, where the SCO transition is accompanied by ar eversible change from ah ighly colored high-spin (HS) state to the pale to colorless low-spin (LS) state.…”

A Two‐Dimensional Iron(II) Coordination Polymer with Synergetic Spin‐Crossover and Luminescent Properties

“…At 20 K, the χ M T value is 0.93 cm 3 mol −1 K, indicating that about 30 % of the Fe II ions still remain in the HS state. The residual HS Fe II in 1⋅3CH 3 OH and 1 may be ascribed to the structural and topological defects . The subsequent heating process demonstrates almost no thermal hysteresis.…”

“…The SCO entity is a better energy acceptor, and the energy transferred to them from donor luminophores is expected to be different for the two different spin states. Thus, the emission characteristics of the luminophore can be modulated upon spin‐state switching; meanwhile, it is achievable to use the reliable and practical optical signal as a probe for the change of spin states …”

Five 2,6-Di(pyrazol-1-yl)pyridine-4-carboxylate Esters, and the Spin States of their Iron(II) Complexes

“…Spin-crossover (SCO) compounds are an important class of molecular switches which are widely studied in molecular materials chemistry [1][2][3]. The SCO switching event changes a number of physical properties in a material including its colour, magnetic moment [4], volume [5], dielectric properties [6][7][8][9], conductivity [9][10][11][12], and fluorescence [13][14][15]. Solid or mesophase phase transitions and isotropic melting can also be coupled to spin transitions in soft materials containing SCO centres [16,17].…”