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

Abstract Luminescent Zn II clusters [Zn 4 L 4 (μ 3 ‐OMe) 2 X 2 ] (X=SCN ( 1 ), Cl ( 2 ), Br ( 3 )) and [Zn 7 L 6 (μ 3 ‐OMe) 2 (μ 3 ‐OH) 4 ]Y 2 (Y=I − ( 4 ), ClO 4 − ( 5 )), HL=methyl‐3‐methoxysalicylate, exhibiting blue fluorescence at room temperature ( λ max =416≈429 nm, Φ em =0.09–0.36) have been synthesised and investigated in detail. In one case the external heavy‐atom effect (EHE) arising the presence of iodide counter anions yielded phosphorescence with a long emission lifetime ( λ max =520 nm, τ =95.3 ms) at 77 K. Single‐crystal X‐ray structural analysis and time‐dependent density‐functional theory (TD‐DFT) calculations revealed that their emission origin was attributed to the fluorescence from the singlet ligand‐centred ( 1 LC) excited state, and the phosphorescence observed in 4 was caused by the EHE of counter anions having strong CH−I interactions.