Plasmonically enhanced Fe(ii) coordination complexes allow SERS readout of spin state switching below the optical...

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Monitoring spin crossover (SCO) materials at the nanoscale presents significant challenges due to perturbed spin transitions and limited detection methods.
• Optical techniques for nanoscale SCO monitoring are hampered by weak signal intensities.

Purpose of the Study:

• To demonstrate a novel method for enhanced readout of spin state transitions in nanoscale SCO materials.
• To investigate the feasibility of using surface-enhanced Raman spectroscopy (SERS) for monitoring SCO phenomena in confined nanostructures.

Main Methods:

• Utilized surface-enhanced Raman spectroscopy (SERS) to probe spin crossover phenomena.
• Employed Au@SCO core-shell nanoparticles to create plasmonic nanovoids.
• Investigated SCO behavior of [Fe(Htrz)2(trz)](BF4) (1) confined within nanogaps.

Main Results:

• Achieved enhanced SERS signals for SCO nano-objects (<1 µm) confined within plasmonic nanovoids.
• Demonstrated that SCO behavior is retained when SCO materials are placed in plasmonic hotspots of Au@SCO core-shell nanoparticle clusters.
• Observed thermal hysteresis loops (9 K) in nanoparticle clusters, indicating retained cooperative behavior, albeit narrower than bulk material (40 K).

Conclusions:

• Surface-enhanced Raman spectroscopy (SERS) is a viable and effective technique for monitoring spin crossover transitions in nanoscale SCO materials.
• Plasmonic nanovoids, specifically within Au@SCO core-shell nanoparticle clusters, can host SCO materials while preserving their cooperative behavior.
• This approach overcomes the limitations of weak signal levels in optical monitoring of nanoscale SCO phenomena.