Carborane-thiol protected copper nanoclusters: stimuli-responsive materials with tunable phosphorescence

Area of Science:

• Materials Science
• Nanotechnology
• Solid-State Chemistry

Background:

• Atomically precise nanomaterials with tunable luminescence are of significant interest.
• Copper nanoclusters (NCs) offer unique electronic and optical properties.

Purpose of the Study:

• To synthesize and characterize a new class of thermally stable, isostructural tetranuclear copper nanoclusters (Cu4 NCs) protected by carborane thiols.
• To investigate the solid-state luminescence properties and stimuli-responsiveness of these novel NCs.

Main Methods:

• Synthesis of Cu4 NCs using ortho-carborane-9-thiol, meta-carborane-9-thiol, and ortho-carborane 12-iodo 9-thiol.
• Structural characterization using HR ESI-MS, collision energy-dependent fragmentation, spectroscopy, and microscopy.
• Photoluminescence spectroscopy to determine emission color, quantum yield, and lifetime.
• Density functional theory (DFT) calculations for electronic structure analysis.
• Mechanical grinding and solvent vapor exposure tests for stimuli-responsiveness.

Main Results:

• Three isostructural Cu4 NCs (Cu4@oCBT, Cu4@mCBT, Cu4@ICBT) were synthesized with a square planar Cu4 core and butterfly-shaped Cu4S4 staple.
• While non-emissive in solution, crystalline NCs exhibited bright, microsecond-long phosphorescence (green for Cu4@oCBT/Cu4@mCBT, orange for Cu4@ICBT).
• Cu4@oCBT and Cu4@mCBT showed mechanoresponsive luminescence, shifting from green to yellow upon grinding and regenerating with solvent vapor. Cu4@ICBT's orange emission was unaffected.
• Cu4@oCBT and Cu4@mCBT demonstrated high thermal stability up to 400°C, with Cu4@oCBT retaining green emission up to 200°C.

Conclusions:

• This work presents the first structurally flexible carborane thiol-appended Cu4 NCs with stimuli-responsive tunable solid-state phosphorescence.
• The findings highlight the potential of these NCs for applications requiring tunable luminescence and responsiveness to external stimuli.
• Structural modifications, such as the introduction of bulky iodine substituents, influence the cluster's geometry and luminescence behavior.