Phosphorescence at Low Temperature by External Heavy-Atom Effect in Zinc(II) Clusters.

Area of Science:

• Coordination Chemistry
• Materials Science
• Photophysics

Background:

• Luminescent metal clusters are of interest for their unique photophysical properties.
• Tuning luminescence through structural modification and external factors is a key research area.

Purpose of the Study:

• To synthesize and characterize novel luminescent zinc(II) clusters.
• To investigate the origin of their luminescence and the effect of counter anions on photophysical properties.

Main Methods:

• Synthesis of zinc(II) clusters with varying counter anions (SCN, Cl, Br, I, ClO4).
• Photoluminescence spectroscopy at room temperature and 77 K.
• Single-crystal X-ray structural analysis.
• Time-dependent density-functional theory (TD-DFT) calculations.

Main Results:

• Five luminescent Zn(II) clusters were synthesized, exhibiting blue fluorescence (λmax = 416–429 nm, Φem = 0.09–0.36).
• Cluster 4, containing iodide anions, showed phosphorescence (λmax = 520 nm, τ = 95.3 ms) at 77 K due to the external heavy-atom effect (EHE).
• TD-DFT calculations attributed emission to singlet ligand-centered (1LC) excited states, with phosphorescence linked to CH-I interactions.

Conclusions:

• The synthesized Zn(II) clusters are efficient blue emitters.
• The external heavy-atom effect, particularly with iodide, can induce phosphorescence and tune luminescence properties.
• Ligand-centered excited states and anion-π interactions play crucial roles in the observed photoluminescence.