Highly Selective Na⁺‐Templated Formation of [2]Pseudorotaxanes Exhibiting Significant Optical Outputs

Abstract

The diverse range of binding geometries exhibited by metal ions and their relatively stable interactions with ligands can be exploited for the efficient template-directed synthesis of macrocycles,[1] supramolecular architectures, [2] and interlocked molecules.[3] Although the formation of rotaxanes or pseudorotaxanes has been demonstrated using transitionmetal ions coordinated to four (tetrahedral and square planar), [4] five (trigonal bipyramidal and square pyramidal), [5] and six (octahedral) [6] donor atoms, alkali-metal ions, which are useful templates for the synthesis of crown ethers, [7] are rarely used to direct the construction of such complexes. In one example, Li + ions have been used to assist the formation of a unique donor-acceptor pseudorotaxane, [8] but it appears that Na + ions play a similar role in that system. [9] We became interested in forming pseudorotaxanes in solution with high efficiency and selectivity toward a single species of alkalimetal ion-especially if we could differentiate between the physiologically important, [10] but chemically similar, Na + and K + ions.[11] Herein, we report a new molecular recognition system based on the molecular cage 1 (Scheme 1) and two different threadlike molecules (anthraquinone and squaraine), each of which forms a pseudorotaxane complex with 1 in the presence of templating Na + ions and exhibits high selectively over the other alkali-metal ions tested. This ionspecific templating effect was easy to monitor because the complexation and decomplexation of the pseudorotaxane complexes in solution occurred with color changes that were detectable to the naked eye. It appears from the solid-state structures that the dramatic Na Previously, we demonstrated that molecular cage 2 and anthraquinone (3, Scheme 2) can form pseudorotaxane-like complexes in solution when K + ions are present. [12] We suspected that greater ion-selective templating behavior would arise if we replaced the two openings resembling dibenzo [24]crown-8 (DB24C8) in 2 with two relatively smaller and more rigid units resembling dibenzo [18]crown-6

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

“…We later reported the alkali metal ion-templated formation of [2]­pseudorotaxanes from squaraine- and anthraquinone-based guests and a molecular cage as the host . The solid-state structures of these two types of [2]­pseudorotaxanes (Scheme ) revealed the chelation of the two CO oxygen atoms of the guest to the Na + ions, which were themselves complexed to the [18]­crown-6 (18C6) openings of the molecular cage.…”

The uptake of metal elements into poly(1-methylpyrrol-2-ylsquaraine) particles and a study of their porosity

“…If either component of ammonium phosphate was chemisorbed onto the surface of the PMPS particles, then the particles, either before or after compounding into polymer fibres, would not consistently leach phosphate over numerous washing events. However, there is evidence, in two previously reported X-ray crystal structures, that squarate oxygen atoms are capable of co-ordination with metals (Hsueh et al., 2007a,b). Thus, direct metal co-ordination with the squarate oxygens in the PMPS pores must also be taken into account, which is suspected, in corporation with the specific pore sizes, to give rise to the differences in metal element uptake.…”

Protecting a Squaraine near-IR Dye through Its Incorporation in a Slippage-Derived [2]Rotaxane

“…Intuitively, use of the slippage approach 6 toward rotaxane synthesis would minimize the squaraine dye's contact with nucleophiles during the rotaxane formation process. Previously, we reported that Na + ions could be used to template the formation of a [2]pseudorotaxane from a squaraine dye and a molecular cage in CH 3 CN . Herein, we report high- yield slippage syntheses of corresponding [2]rotaxanes from this unique Na + ion-templated recognition system and the photophysical properties and enhanced chemical stability of the encircled squaraine dye.…”