Vibration-Dependent Dual-Phosphorescent Cu₄ Nanocluster with Remarkable Piezochromic Behavior

Area of Science:

• Nanomaterials Science
• Photochemistry
• Solid-State Chemistry

Background:

• Dual emission (DE) in atomically precise copper nanoclusters (Cu NCs) is of significant interest, but the underlying mechanism remains unclear.
• Excited state processes in Cu NCs are complex, hindering a full understanding of their photophysical properties.

Purpose of the Study:

• To synthesize a novel alkynyl-shielded copper nanocluster exhibiting dual emission.
• To investigate the mechanism of dual emission in Cu NCs using hydrostatic pressure for the first time.

Main Methods:

• Synthesis of a novel [Cu₄(PPh₃)₄(C≡C-p-NH₂C₆H₄)₃]PF₆ (Cu₄) nanocluster.
• Application of hydrostatic pressure to study changes in emission properties and crystal structure.
• Angle-dispersive synchrotron X-ray diffraction to analyze structural changes under pressure.
• In situ high-pressure Raman and vibrationally resolved emission spectroscopy.

Main Results:

• The synthesized Cu₄ nanocluster exhibited dual emission and piezochromism (cyan to orange).
• Increasing pressure caused the higher-energy emission peak to vanish, with strengthened hydrogen bonds (C-H⋅⋅⋅N, N-H⋅⋅⋅N) observed.
• Angle-dispersive synchrotron X-ray diffraction showed reduced inter-cluster distances and closer peripheral ligands under pressure.
• Spectroscopic analysis identified benzene ring C=C stretching vibration as the source of DE.

Conclusions:

• Hydrostatic pressure can modulate the dual emission properties of Cu NCs.
• Strengthened hydrogen bonding and ligand vibrations play a crucial role in the dual emission mechanism.
• The benzene ring C=C stretching vibration is identified as the structural origin of dual emission in these Cu NCs.