16–20 They display different magnetic property depending on the stpy ligand, and the SCO temperature is up to about 300 K for X = BH 3. 12–15 Among the Fe-based LD-LISC SCO systems, the family of Fe(stpy) 4(NCX) 2 (X = S, Se, and BH 3, stpy = cis- or trans-styrylpyridine isomers) complexes is of particular interest. Many promising photoactive ligands in these LD-LISC systems including stilbene, azobenzene, diarylethene, and styrylpyridine, have been successfully synthesized. 9–11 These compounds always present the spin transition upon the conformational changes via the reversible cis– trans isomerization or ring-closing/ring-opening reactions under electromagnetic radiation, and then they exhibit the so-called ligand-driven light-induced spin-change (LD-LISC) effect. up to room temperature), have been driven more attention in molecular spin switch. Fortunately, a family of SCO systems containing photoactive ligands, which can work at high temperature ( i.e. 7,8 In practical applications, the SCO complexes spin switch should ideally operate under atmospheric pressure and at room temperature. Nevertheless, until now their applications are prohibited since the lifetimes of the photomagnetic states are long enough only at low temperature. In experiments, one of the possible mechanisms for the observed SCO behavior is the light-induced excited spin state trapping (LIESST) effect, which is encountered in many Fe-based SCO complexes. Therefore, more attention should be paid to the transport properties of these Fe-based SCO complexes. 5,6 Due to the different electronic configurations of the 3d electrons, these Fe-based complexes with the HS and LS states display the dramatically different optical, electronic, and magnetic properties, and they are considered as promising candidates for future applications, such as sensor, display, information storage and molecular spintronic devices. 1–4 The switching between the LS and HS states has been observed in many SCO complexes of d 4–d 7 transition metal ions, but the Fe-based SCO complexes (d 6) account for more than 90% of known SCO materials. The most interesting and investigated feature of spin-crossover (SCO) complexes, formed by metal ions in surrounding ligands, is the transition between the low-spin (LS) (usually the ground state) and high-spin (HS) states of the central metal ion, which can be triggered by temperature, pressure, and light as well as electric and magnetic fields. These obtained theoretical findings suggest that the examined Fe-based LD-LISC SCO complexes hold great potential in molecular spintronics. Remarkably, we observe the nearly perfect spin-filtering effect and obvious negative differential resistance feature in the Fe(stpy) 4(NCX) 2 junctions with the trans and cis configurations, which is attributed by the dramatically different electronic structures of two spin channels and the bias-dependent transmission spectra, respectively. As for the trans configuration, the current through the molecular junction with the HS state is significantly larger than that of the LS state, which indicates that this Fe-based LD-LISC SCO complex with the trans configuration could act as a molecular switch when the spin transition is triggered by external stimuli. Here, we explore the transport properties of Fe(stpy) 4(NCS) 2 LD-LISC SCO complexes with the trans and cis configurations sandwiched between Au electrodes by performing extensive density functional theory calculations combined with the non-equilibrium Green's function method. ![]() The Fe-based spin-crossover (SCO) complexes, especially the ligand-driven light-induced spin-change (LD-LISC) systems with high spin-transition temperature, are considered as the most promising building blocks for designing molecular spintronic devices due to their bistability between the high-spin (HS) and low-spin (LS) states.
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