Photoinduced hydrogen-bonded self-assembly of cation-capped complexes and novel photoswitchable supramolecular devices based on (aza)-18-crown-6-containing styryl dyes bearing a long N-ammonioalkyl substituent

Abstract

E-Isomers of styryl dyes containing a benzo-18-crown-6 ether or N-methylbenzoaza-18-crown-6 ether moiety and a benzothiazolium residue with an ammoniohexyl, ammoniopentyl, or ammoniomethylbenzyl N-substituent were synthesized. According to spectrophotometry and NMR spectroscopy data, dyes of this type are capable of self-assembly in MeCN to form dimeric complexes, which have a pseudocyclic structure owing to double intermolecular ammonium cation–crown ether interactions via hydrogen bonds; the dimerization equilibrium constants were measured. It was shown that photoinduced Z-isomers of the dyes are capable of intramolecular complex formation between the ammonium cation and the crown ether moiety; therefore, upon E→Z photoisomerization, the dimer–monomer equilibrium shifts towards the pseudocyclic monomer. Data on the relative stability of the intramolecular cation-capped complexes formed by Z-isomers were obtained. It was shown that the equilibrium constants for the Ba²⁺ complexation with E-isomers of the dyes are almost three orders of magnitude higher than those for that with Z-isomers, which may imply the applicability of these dyes as photoswitchable supramolecular devices.