Build 3D Nanoparticles by Using Ultrathin 2D MOF Nanosheets for NIR Light-Triggered Molecular Switching

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Spin-crossover (SCO) materials exhibit distinct high-spin (HS) and low-spin (LS) states.
• Ultrathin 2D nanosheets of metal-organic frameworks (MOFs) offer unique properties but face challenges in solid-state performance.
• Controlling SCO material assembly is crucial for optimizing their responsiveness.

Purpose of the Study:

• To investigate the effect of assembling 2D SCO nanosheets into 3D nanoparticles on SCO performance.
• To explore the potential of near-infrared (NIR) light for triggering SCO transitions.
• To demonstrate NIR-triggered molecular conversion under ambient conditions.

Main Methods:

• Synthesized ultrathin 2D spin-crossover (SCO) nanosheets of {[Fe(1,3-bpp)2(NCS)2]2} MOFs.
• Assembled 2D nanosheets into 3D nanoparticles via coordination interactions with transition-metal ions (Cu2+, Ag+).
• Loaded SCO nanoparticles onto ytterbium ion (Yb3+)-sensitized upconverting nanoparticles and investigated NIR light response.

Main Results:

• 3D nanoparticle assembly significantly altered electronic transitions (π-π* and metal-to-ligand charge transfer) compared to 2D nanosheets, with dramatic blue-shifts observed.
• A d-d transition band for high-spin (HS) state Fe(II) ions was generated in 3D nanoparticles, indicating dimensional influence on SCO.
• NIR light (980 nm) successfully triggered HS to LS state transitions in SCO nanoparticles dispersed in aqueous suspension.

Conclusions:

• Assembling 2D SCO nanosheets into 3D nanoparticles profoundly enhances solid-state SCO performance.
• The study achieved the challenging goal of NIR light-triggered molecular spin conversion under ambient conditions.
• This work opens avenues for developing advanced materials for light-responsive molecular devices.