Tautomeric chromoionophores derived from 1-aryloxyanthraquinones and 4′-aminobenzo-15-crown-5 ether: Sandwich complex formation enhanced by interchromophoric interactions

A series of tautomeric chromoionophores were prepared photochemically from 1-aryloxyanthraquinones and 4′-aminobenzo-15-crown-5 ether. All the synthesized dyes can bind strontium and barium cations as sandwich-type 2:1 ligand-metal complexes that show higher stability constants (K2:1) than the corresponding 1:1 complexes (K1:1), the K2:1/K1:1 ratio reaching a value of 10 (in MeCN). The inverse relation, i.e. K2:1 < K1:1, is observed for the related complexes of unsubstituted benzo-15-crown-5 ether. The sandwich complexes were studied by spectrophotometry, 1H NMR spectroscopy, mass spectrometry, and density functional theory calculations. A correlation was found between the K2:1/K1:1 ratio and the number of short stacking contacts in the sandwich complex.

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