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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Liquid crystalline phase transition induces spin crossover in a polyelectrolyte amphiphile complex
Yves Bodenthin1, Guntram Schwarz, Zbigniew Tomkowicz
1University Siegen, FB7 Solid State Physics, D-57068 Siegen, Germany.
Journal of the American Chemical Society
|February 12, 2009
Summary
Iron and nickel metallosupramolecular polymers form liquid crystals. Heating Fe-PAC induces irreversible spin-crossover (SCO) with a color change, while Ni-PAC shows no SCO. Dissolving recovers the original state.
Area of Science:
- Coordination Chemistry
- Materials Science
- Supramolecular Chemistry
Background:
- Metallosupramolecular coordination polyelectrolytes (MEPE) are formed by self-assembly of metal ions and ligands.
- Incorporating amphiphiles like dihexadecyl phosphate (DHP) creates polyelectrolyte amphiphile complexes (PACs) with liquid crystalline properties.
Purpose of the Study:
- To investigate the spin-crossover (SCO) behavior in Fe-PAC and Ni-PAC systems.
- To understand the relationship between structural changes, thermal properties, and magnetic transitions.
- To compare the SCO behavior in PACs versus neat MEPE.
Main Methods:
- Self-assembly of Fe(II) or Ni(II) ions with 6,6',6''-bis(2-pyridyl)-2,2':4',4'':2'',2'''-quaterpyridine (btpy) to form MEPE.
- Sequential assembly with dihexadecyl phosphate (DHP) to form PACs.
- Thermal analysis (thermogravimetric analysis, differential scanning calorimetry) and magnetic measurements.
Main Results:
- Fe-PAC exhibits an irreversible, near-complete (95%) spin-crossover from low-spin to high-spin state upon heating, accompanied by a color change.
- The SCO in Fe-PAC is linked to the melting of the amphiphilic matrix and associated structural changes.
- Fe-PAC does not reassemble upon cooling but can be recovered by dissolution; Ni-PAC shows similar structural changes but no SCO.
Conclusions:
- The liquid crystalline matrix in Fe-PAC is crucial for enabling a complete and irreversible SCO.
- In contrast, the solid-state architecture of Fe-MEPE restricts structural changes, leading to incomplete SCO dependent on sample history and solvent content.
- This study highlights the role of the amphiphilic matrix in controlling SCO properties in metallosupramolecular materials.
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