Playing with Polyoxometalates to Build Molecular Materials Exhibiting Negative Solid-State Photochromism

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Photochemistry

Background:

• Polyoxometalates (POMs) are versatile inorganic clusters with tunable electronic and structural properties.
• Spiropyrans are photochromic molecules that undergo reversible structural transformations upon light irradiation.
• Combining POMs and spiropyrans offers opportunities to develop novel functional materials with unique optical properties.

Purpose of the Study:

• To synthesize and characterize novel ionic assemblies of POMs and cationic spiropyran SPPy+.
• To investigate the solid-state photochromic behavior of these hybrid materials.
• To explore the influence of POM structure and synthesis conditions on photochromic performance.

Main Methods:

• Synthesis of four novel POM/Spiro ionic assemblies.
• Structural characterization using X-ray diffraction.
• Solid-state 13C NMR spectroscopy to determine merocyanine form proportion.
• Investigation of photochromic properties, including coloration and fading kinetics.

Main Results:

• Four new POM/Spiro ionic assemblies were successfully synthesized and characterized.
• Two assemblies, (SPPy)2[W6O19]·2CH3CN and (SPPy)3.7(H)0.3[β-Mo8O26], exhibited strong photocontrast.
• These two materials demonstrated solid-state negative photochromism, returning to a colored state in the dark after discoloration.
• Non-photochromic behavior was observed in other synthesized assemblies under similar conditions.

Conclusions:

• The nature of the POM and synthesis conditions critically influence the optical properties of POM/Spiro hybrid materials.
• The first examples of solid-state negative photochromism in POM/Spiro hybrid materials were achieved.
• These findings open new avenues for designing advanced photoresponsive materials.