Hexamethoxycalix[6]arene 3 forms a directional pseudorotaxane complex with the chiral axle (S)-(α-methyl-benzyl)benzylammonium 2+. Between two (endo-chiral)-2+@3 and (exo-chiral)-2+@3 stereoisomers, former is preferentially formed. This result confirms validity of “endo-α-methyl-benzyl rule”, previously reported by us. DFT calculations suggest that C-H···π interactions between methyl group 2+ c...

Octa acid (OA), a calixarene-based cavitand, forms a 1:2 capsular assembly with neutral 1,3,3-trimethyl-6'-nitrospiro[2H-1]benzopyran-2,2'-indoline and 1:1 cavitandplex with its open zwitterionic merocyanine form. Photochromic interconversion between the spiropyran and merocyanine leads to unprecedented reversible capsular disassembly and assembly. OA provides stability to the merocyanine in bo...