Green‐Emissive Zn 2+ Complex Supported by a Macrocyclic Schiff‐Base/Calix[4]arene‐Ligand: Crystallographic and Spectroscopic Characterization

The macrocyclic calix[4]arene ligand H 2 L comprises two non‐fluorescent 2,6‐bis‐(iminomethyl)phenolate chromophores, which show a chelation‐enhanced fluorescence enhancement upon Zn 2+ ion complexation. Macrocyclic [ZnL] complexes aggregate in the absence of external coligands via intermolecular Zn−N bonds to give dimeric [ZnL] 2 structures comprising two five‐coordinated Zn 2+ ions. The absorption and emission wavelengths are bathochromically shifted upon going from the liquid (λ max,abs (CH 2 Cl 2 )=404 nm, λ max,em (CH 2 Cl 2 )=484 nm) to the solid state (λ max,abs =424 nm (4 wt%, BaSO 4 pellet), λ max,em =524 nm (neat solid)). Insights into the electronic nature of the UV‐vis transitions were obtained with time‐dependent density functional theory (TD‐DFT) calculations for a truncated model complex.