From the host-guest chemistry mentioned above, it is evident that cage
1 selectively encapsulate PHE over its isomer ANT. Multiple attempts to crystallize the host-guest complexes have failed. Molecular mechanical modeling (Fig. S26 in Supporting information) suggests that PHE⊂
1 is more geometrically favorable than ANT⊂
1 due to the presence of additional CH···
π interactions between PHE guests and the macrocycle host compared to the hypothetical ANT⊂
1 complex. According to the literature [
87], the solubility of PHE (8.1 × 10
−3 mmol/L) is about 21 times higher than that of ANT (3.9 × 10
−4 mmol/L) in water. It is possible that such a difference in solubility may also contributed to the selective binding of PHE over ANT. These unexpected discoveries position cage
1 as a more favorable water-soluble supramolecular host for separating PHE from isomeric mixtures of PHE and ANT, as illustrate in
Fig. 4a. Firstly, we conducted a competitive encapsulation experiment between PHE and ANT within cage
1. Initially, clear PHE⊂
1 solution was treated with 3 equiv. of ANT and stirred for 1 h at room temperature. After the removal of the solid, the resulting clear solution exhibited nearly unchanged
1H NMR signals of PHE⊂
1 (
Figs. 4b and
c and Fig. S44 in Supporting information). In reverse, the equivalent amount of PHE was added into the resulting mixture of cage
1 and 3 equiv. of ANT after stirring for 1 h.
1H NMR signals also clearly indicated that the host-guest signals were consistent with PHE⊂
1 (
Fig. 4e and Fig. S43 in Supporting information). Furthermore, when 3 equiv. of ANT and 3 equiv. of PHE were simultaneously added into the aqueous solution of cage
1, the supernatant obtained after centrifugation exhibited the identical signals to that of PHE⊂
1 with no detectable ANT observed in the
1H NMR (
Fig. 3d and Fig. S45 in Supporting information). These results clearly indicated that
1 selectively captured PHE from the mixture of PHE and ANT. The trapped PHE can be released by extracting the clear aqueous solution with chloroform, resulting in a high purity of 99% PHE, as detected by the
1H NMR spectrum using trimethoxy benzene as an internal standard. Additionally, the successfully recovered empty
1 in aqueous state was also evidenced by the
1H NMR spectrum. Moreover, the recovered
1 can be reused for subsequent separations of PHE from the mixture. We found that cage
1 can be recycled up to 5 times without loss of its performance in selectivity (99%) (
Fig. 4h and Fig. S46 in Supporting information), suggesting that
1 was a stable and robust material for the selective separation of PHE. Compared with previous works on the separation of the isomer mixture [
72,
73], our cage exhibits equal or higher purity of PHE (
Fig. 4i). Furthermore, our cage
1 selectively removed a small amount of PHE (10%) from ANT (90%), resulting in an impressive purity exceeding 99.9% (Figs. S47 and S48 in Supporting information). These findings demonstrate that cage
1 holds promise as an excellent candidate for the separation of the isomer mixture.