Four- and two-armed hetero porphyrin dimers: their specific recognition and self-sorting behaviours. Issue 2 (15th December 2021) - Ueda, Masahiro
Abstract : Self-assembled/self-sorted hetero dimer capsules consisting of pairs of two- and four-armed porphyrins were constructed. Small and large aromatic guests were selectively recognized by two- and four-armed dimers, respectively. Abstract : In this study we self-assembled the four-armed porphyrin hetero dimer capsule Cap4, stabilized through amidinium–carboxylate salt bridges, in CH2 Cl2 and CHCl3 . The dimer capsule Cap4 was kinetically and thermodynamically more stable than the corresponding two-armed dimer Cap2 . The number of arms strongly influenced their recognition behaviour; guests possessing small aromatic faces ( e.g., 1, 3, 5-trinitrobenzene) preferred residing in the cavity of the two-armed capsule Cap2, rather than in Cap4, both thermodynamically and kinetically; in contrast, large aromatic guests ( e.g., 9, 10-dibromoanthracene) were encapsulated predominantly by Cap4 because of favourable entropic effects. The number of arms enabled self-sorting behaviour of the dimer formation; complexation studies using an equimolar mixture of the four porphyrin constituents of the two capsules revealed the quantitative formation of the corresponding dimers Cap2 and Cap4 . Furthermore, we examined the specific molecular recognition of Cap2 and Cap4 ; NMR experiments of mixtures of Cap2 and Cap4 in the presence of favourable guests for Cap2 and Cap4 revealed that these guest molecules were encapsulated selectively by their preferred hosts.