Green-Emissive Zn2+ Complex Supported by a Macrocyclic Schiff-Base/Calix[4]arene-Ligand: Crystallographic and Spectroscopic Characterization

Abstract

The macrocyclic calix[4]arene ligand H2L comprises two non-fluorescent 2,6-bis-(iminomethyl)phenolate chromophores, which show a chelation-enhanced fluorescence enhancement upon Zn2+ 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 Zn2+ ions. The absorption and emission wavelengths are bathochromically shifted upon going from the liquid (λmax,abs (CH2Cl2)=404 nm, λmax,em (CH2Cl2)=484 nm) to the solid state (λmax,abs=424 nm (4 wt%, BaSO4 pellet), λmax,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.