Ion‐Pairing Effects in the Self‐Assembly of a Fluorescent Pseudorotaxane

Abstract

AbstractHerein we report on the self‐assembly, in a low polarity solvent, of a pseudorotaxane species comprising binaphthyl‐26‐crown‐8 (BN26C8) as the macrocyclic host and anthracenyl‐benzylammonium as the threadlike positively charged guest (ABH+). Absorption and luminescence data reveal a very efficient energy transfer process occurring from the binaphthyl to the anthracene singlet excited states. The self‐assembly is highly dependent on the nature of the counteranion confirming the crucial role played by it in the competition between the self‐assembly process and the formation of ion pairs (ABH+X–). This behavior can be readily evidenced in dilute solutions from the analysis of the luminescence properties of the system. The complexation of chloride, sulfate and hexafluorophosphate salts of ABH+ by racemic BN26C8 as well as the complexation of ABH+ salts of the chiral anion tris[tetrachlorobenzenediolato]phosphate(V) (TRISPHAT–) by (+)BN26C8 are described. The efficiency in complexation follows the trend PF6– > TRISPHAT– > Cl–, SO42–. The use of the chiral anion TRISPHAT allowed us to investigate the possibility of inducing stereoselective control on the formation of the interpenetrating assembly. Preliminary 1H NMR spectroscopic evidence supports the fact that the chiral anion is paired to the supramolecular complex and that its configuration influences the recognition process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)