Ion-pairing effects in the self-assembly of a fluorescent pseudorotaxane

Herein 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 anthracenylbenzylammonium 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 hexa-fluoride phosphate salts of ABH(+) by racemic BN26C8 as well as the complexation of ABH(+) salts of the chiral anion tris[tetra robenzenediolatolphosphate(v) (TRISPHAT(-)) by (+) BP 8 are described. The efficiency in complexation following the trend PF6- > TRISPHAT(-) > Cl- SO42-. The use of the central anion TRISPHAT allowed us to investigate the possibility of inducing stereoselective control on the formation of counterpenetrating assembly. Preliminary H-1 NMR spectroscopic evidence supports the fact that the chiral anion is pa to the supramolecular complex and that its configuration influences the recognition process. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).