Abstract
Aiming at constructing photoresponsive spin crossover (SCO) behavior, herein we designed a new ligand Abtz (Abtz = (E)-N-(4-((E)-phenyldiazenyl)phenyl)-1-(thiazol-4-yl)methanimine) which was decorated by a photochromic azobenzene group. Based on this photochromic ligand, a mononuclear Fe(II) SCO molecule [Fe(Abtz)3](BF4)2·(EAC)2 (1, EAC = ethyl acetate) was successfully synthesized and showed a complete one-step SCO behavior. Under continuous UV light and blue-light exposure, the cis–trans photoisomerization of both ligand Abtz and compound 1 in the liquid phase was confirmed through UV–Vis spectra. Moreover, the 1H-NMR spectra of Abtz reveal a trans–cis conversion ratio of 37%. Although the UV–Vis spectra reveal the photochromic behavior for 1 in the solution phase, the SCO behavior in the liquid state is absent according to the variable-temperature Evans method, suggesting the possible decomposition. Moreover, in the solid state, the cis–trans photoisomerization of both Abtz and 1 was not observed, due to the steric hindrance.
Highlights
Complexes [1–6] of 3d4~7 transition metal ions have attracted intense interest from scientists due to their fascinating multi-functional properties on nonlinear optical [7], magnetism [8], conductivity [9–12] and mechanical properties [13], which result from the d-orbital electron rearrangement between the low-spin (LS) and high-spin (HS) electronic configurations under external stimuli, e.g., heat, optical and pressure
A series of spin crossover (SCO) compounds decorated by photochromic groups, showing cis–trans photoisomerization behavior [19,20], intramolecular photocyclization [21–24] and photochemical [2 + 2] cycloaddition [25,26], which were reported in Molecules 2022, 27, 1571 groups, showing cis–trans photoisomerization behavior [19,20], intramolecular photocyclization [21–24] and photochemical [2+2] cycloaddition [25,26], which were report2edof 1in1 recent years, and the corresponding photoresponsive SCO behaviors were further studied in the solid or liquid state
The IR spectra were maintained unchanged under further blue-light irradiation. For further studying this behavior, we performed the Powder X-ray diffraction (PXRD) measurement for compound 1 under different UV irradiation times (Figure 7c) and found that the crystalline phase gradually disappeared with the lengthening of the irradiation time
Summary
Complexes [1–6] of 3d4~7 transition metal ions have attracted intense interest from scientists due to their fascinating multi-functional properties on nonlinear optical [7], magnetism [8], conductivity [9–12] and mechanical properties [13], which result from the d-orbital electron rearrangement between the low-spin (LS) and high-spin (HS) electronic configurations under external stimuli, e.g., heat, optical and pressure This ability of spin crossover (SCO) compounds to tune their functional properties shows potential applications in the fields of information storage, sensors and actuators. Zarembowitch et al put forward the ligand-driven light-induced spin crossover (LD-LISC) approach [15–18], showing the possibility to switch the spin state through generating different ligand fields around the SCO center from the two isomeric forms of photoreactive ligands. Hstoawtese,vienrd, dicuaetitnogtahne ipnoesrstibLlDe -dLeIcSoCmbpeohsaivtiioonr.in the liquid state and steric hindrance in the solid state, the cis–trans photoisomerization of 1 is not observed in both liquid and solid s2t.aRteess,uinltdsicating an inert LD-LISC behavior
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