Crown-ether- and porphyrin-attached gel-phase resins in thermodynamically controlled rotaxane assembly

Abstract

Results of gel-phase proton high resolution magic angle spinning (HR MAS) NMR spectroscopy are described for a systematic study of the reversible, thermodynamically-controlled assembly of surface-attached neutral rotaxanes and pseudorotaxanes based on a three-component system consisting of a naphthodiimide thread unit, a naphthalene crown shuttle, and metalloporphyrin stoppers. Further to the previous systems based on an immobilised thread unit, we report here on the alternative systems where firstly a crown shuttle unit, and secondly metalloporphyrin stopper units, are attached to polystyrene beads, with the other two rotaxane components supplied in the surrounding solution phases in each case. Variations in concentration, temperature, and the effects of the addition of alkali metal salts are investigated. Within some limitations imposed by the technique itself, these results confirm that for each of the single entities attached in turn to polystyrene beads, rotaxane formation parallels that observed in the analogous solution-phase systems.