A Mononuclear Iron(II) Spin-Crossover Molecule Decorated by Photochromic Azobenzene Group

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Photochemistry

Background:

• Spin crossover (SCO) molecules exhibit potential for advanced electronic and sensing applications.
• Photoresponsive materials offer dynamic control over molecular properties.
• Integrating photochromic units into SCO frameworks is a key strategy for light-tunable SCO behavior.

Purpose of the Study:

• To design and synthesize a novel photochromic ligand (Abtz) incorporating an azobenzene group.
• To construct a mononuclear iron(II) SCO complex using the Abtz ligand.
• To investigate the photoresponsive spin crossover behavior of the synthesized complex.

Main Methods:

• Ligand design and synthesis of Abtz ((E)-N-(4-((E)-phenyldiazenyl)phenyl)-1-(thiazol-4-yl)methanimine).
• Synthesis of the mononuclear Fe(II) SCO complex [Fe(Abtz)3](BF4)2·(EAC)2 (1).
• UV-Vis spectroscopy to confirm photoisomerization in solution.
• 1H-NMR spectroscopy to quantify ligand trans-cis conversion.
• Variable-temperature Evans method to study SCO behavior.

Main Results:

• Successful synthesis of the mononuclear Fe(II) SCO complex [Fe(Abtz)3](BF4)2·(EAC)2 (1).
• UV-Vis spectroscopy confirmed cis-trans photoisomerization of Abtz and complex 1 in solution upon UV and blue light exposure.
• 1H-NMR revealed a 37% trans-cis conversion ratio for the Abtz ligand.
• Absence of SCO behavior in the liquid state for complex 1, potentially due to decomposition.
• Lack of observed photoisomerization in the solid state for Abtz and complex 1.

Conclusions:

• The synthesized Abtz ligand exhibits photochromic properties, undergoing cis-trans isomerization in solution.
• The mononuclear Fe(II) complex 1 displays photochromism in solution but lacks observable SCO behavior in the liquid state.
• Steric hindrance prevents photoisomerization in the solid state.
• Further investigation is needed to understand the absence of SCO behavior in solution and explore solid-state photoresponsive SCO.