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Rigid linear compounds G1 and G2, which contained two 4-phenylpyridinium (PhPy+) units, have been prepared to investigate their binding with cucurbit[8]uril (CB[8]). X-ray crystallographic structures revealed that in the solid state both compounds were included by CB[8], through antiparallel stacking, to form 2:2 quaternary complexes (G1)2@(CB[8])2 and (G2)2@(CB[8])2. For the former complex, CB[8] entrapped G1 by holding two heterodimers of its Py + and benzyl units, which were at opposite ends of the backbone. In contrast, for the first time, the second complex disclosed parallel stacking of two cationic Py + units of G2 in the cavity of CB[8] in the solid state, despite the generation of important electrostatic repulsion. Isothermal titrations in water afforded high apparent association constants of 4.36x 106 and 6.43 x 106 M-1 for 1:1 complexes G1@CB[8] and G2@CB[8], respectively, and 1H NMR spectroscopy experiments in D2O confirmed a similar stacking pattern to that observed in the solid state. A previous study and crystal structures of the 2:1 complexes formed between three new controls, G3-5, and CB[8] did not display such unusual stacking of the cationic Py+ unit; this may be attributed to the multivalency of the two CB[8] encapsulation interactions. [ABSTRACT FROM AUTHOR]

A benzene/naphthalene alternately incorporated amide polymer was synthesized and characterized. 1H NMR spectroscopy, fluorescence, and circular dichroism (CD) experiments indicated that, in chloroform, the polymer could be induced by the chiral l-aspartic acid dianion or one of its derivatives to form a helical tubular conformation with twist-sense bias. CD titration studies showed that the l-aspartic acid dianion (8 equiv.) could lead to a maximum Cotton effect. It was also revealed that the twist-sense bias obeyed the majority rule, and 70 % enantiomeric excess could realize the maximum helicity bias. Adding acetonitrile to the solution of chloroform caused inversion of the guest-induced helicity bias of the polymer. [ABSTRACT FROM AUTHOR]

Two water-soluble para-xylylene-connected 4,4′-bipyridinium (BIPY2+) polymers have been prepared. UV-Vis absorption, 1H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY2+ units in the polymers form stable 1:1 charge-transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge-transfer complexes are stabilized by the donor-acceptor interaction between electron-rich TTF and electron-deficient BIPY2+ units and electrostatic attraction between the dicationic BIPY2+ units and the anionic carboxylate groups attached to the TTF core. On the basis of UV-Vis experiments, a lower limit to the apparent association constant of the TTF⋅BIPY2+ complexes of the mixtures, 1.8×106 m−1, has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di- and tetracarboxylic acids to the BIPY2+ molecules and polymers. Moreover, the stability of the charge-transfer complexes formed by the BIPY2+ units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY2+ controls and the dicarboxylate-TTF donor; this has been attributed to the mutually strengthened electron-deficient nature of the BIPY2+ units of the polymers due to the electron-withdrawing effect of the BIPY2+ units. [ABSTRACT FROM AUTHOR]

Two chiral (A)6B-typed supramolecular cages were constructed from hydrogen-bonded C6-symmetric zinc porphyrin hexamers and chiral C3-symmetric pyridyl hexadentates with a core of 1,3,5-triphenylbenzene. Circular dichroism and molecular simulations revealed that the symmetry of the supramolecular cages switched from pseudo- C3 v to C3 with the rotational confinement of the biphenyl backbones at low temperatures, which generated conformationally chiral transfer and amplification. This unique phenomenon suggests a new strategy to develop smart materials with high sensitivity and excellent reversibility. [ABSTRACT FROM AUTHOR]

Aromatic stacking has played a significant role in the design of discrete supramolecular systems. However, for many years, the stacking of conjugated radical cations has been considered only as a novelty due to its weakness. In recent years, it has been demonstrated that the stacking of conjugated radical cations, particularly those formed by bipyridinium or tetrathiafulvalene, can be enhanced remarkably when they are incorporated into rationally designed, preorganized frameworks or entrapped into a confined space. This Focus Review highlights the recent advance in its application as an emerging non-covalent force for the construction of various supramolecular structures. [ABSTRACT FROM AUTHOR]

Compounds 1 a and 1 b were prepared by appending two tetrathiafulvalene (TTF) units to an aromatic amide segment that is driven by six or two intramolecular NH⋅⋅⋅O hydrogen bonds to adopt a folded conformation. UV/Vis absorption experiments revealed that if the TTF units were oxidized to TTF.+ radical cations, the two compounds could form a stable single molecular noncovalent macrocycle in less polar dichloromethane or dichloroethane or a bimolecular noncovalent macrocycle in a binary mixture of dichloromethane with a more polar solvent owing to remarkably enhanced dimerization of the TTF.+ units. The stability of the (TTF.+)2 dimer was evaluated through UV/Vis absorption, electron paramagnetic resonance, and cyclic voltammetry experiments and also by comparing the results with those of control compound 2. The results showed that introduction of the intramolecular hydrogen bonds played a crucial role in promoting the stability of the (TTF.+)2 dimer and thus the noncovalent macrocyclization of the two backbones in both uni- and bimolecular manners. [ABSTRACT FROM AUTHOR]