No abstract

Optical and x‐ray experiments showed the possibility of studying 4‐styrylpyridine with a 15‐crown‐5 ether fragment to bind metal cations through the participation of two centres: the crown ether moiety and the heterocyclic part. The metal cations studied can be divided into three groups. Alkaline earth metal cations form complexes with the crown ether centre, H+, Co2+ and Cd2+ prefer coordination with the N‐atom of heterocyclic part and Hg2+ cations form complexes through coordination with both binding centres. Copyright © 2005 John Wiley & Sons, Ltd.

Styryl dyes 4a-e containing a 15-crown-5 ether unit and a quinoline residue with a sulfonatoalkyl or sulfonatobenzyl N-substituent were synthesized. The relationship between the photochemical behavior of these dyes and their aggregates derived from complexation with Mg(2+) in MeCN was studied using (1)H NMR and absorption spectroscopy. The E-isomers of 4a-e were shown to form highly stable dimeric (2:2) complexes with Mg(2+). Upon irradiation with visible light, the dimeric complexes undergo two competing photoreactions, viz., geometric E --> Z isomerization, resulting in an anion-capped 1:1 complex of the Z-isomer with Mg(2+) and stereospecific syn-head-to-tail [2+2]-cycloaddition, affording a single isomer of bis-crown-containing cyclobutane. The N-substituent in the dye has a dramatic effect on the photochemical behavior of the dimeric complex. Molecular dynamics and semiempirical quantum-chemical calculations were carried out to interpret the observed photocycloaddition in the dimer. Conformational equilibria for the dimer of (E)-4b were analyzed using (1)H NMR spectroscopy.