- Water-soluble meta-poly(phenylene ethynylene) oligomers with stable helical secondary structure
-
Two novel water-soluble meta-poly(phenylene ethynylene) (mPPE) copolymers were synthesized and characterized, each contained ester and amine functional groups attached to exohelix positions on the phenylene rings and one contained methoxy endohelix functi
- Nguyen, Ha H.,McAliley, James H.,Bruce, David A.
-
p. 2019 - 2028
(2012/07/13)
-
- Single-site modifications and their effect on the folding stability of m-phenylene ethynylene oligomers
-
(Equation presented) The folded structure of a m-phenylene ethynylene oligomer is tolerant to single-site modifications to both the backbone sequence and end groups. The helical structure is reinforced by multiple noncovalent interactions, allowing the ol
- Goto, Hirofumi,Heemstra, Jennifer M.,Hill, David J.,Moore, Jeffrey S.
-
p. 889 - 892
(2007/10/03)
-
- Synthesis and self-association of an imine-containing m-phenylene ethynylene macrocycle
-
The purpose of this study was to test the suitability of the imine bond as a structural unit within the backbone of phenylene ethynylene macrocycles and oligomers by determining the ability of m-phenylene ethynylene macrocycle 1 to form π-stacked aggregates in both solution and the solid state. Macrocycle 1, with two imine bonds, was synthesized in high yield from diamine 4 and dialdehyde 5. The imine-forming macrocyclization step was carried out under a variety of conditions, with the best yield obtained simply by refluxing the reactants in methanol. The self-association behavior of 1 in various solvents was probed by 1H NMR. The association constants (KE) in acetoned6 and tetrahydrofuran-d8 were determined by fitting the concentration-dependent chemical shifts with indefinite self-association models. The results showed that solvophobically driven intermolecular π-π stacking could be preserved in the imine-containing m-phenylene ethynylene macrocycles. Interestingly, in acetone macrocycle 1 exhibited a stronger tendency to form a dimer rather than higher aggregates. We postulate that this behavior may be due to electrostatic attraction between dipolar imine groups. The solid-state packing of 1 was studied by wide- and small-angle X-ray powder diffraction (WAXD and SAXD). Bragg reflections of 1 were consistent with a hexagonal packing motif similar to our previous studies on m-phenylene ethynylene macrocycles that formed columnar liquid crystal phases.
- Zhao, Dahui,Moore, Jeffrey S.
-
p. 3548 - 3554
(2007/10/03)
-
- m-Diethynylbenzene macrocycles: Syntheses and self-association behavior in solution
-
m-Diethynylbenzene macrocycles (DBMs), buta-1,3-diyne-bridged [4n]metacyclophanes, have been synthesized and their self-association behaviors in solution were investigated, Cyclic tetramers, hexamers, and octamers of DBMs having exo-annular octyl, hexadecyl, and 3,6,9-trioxadecyl ester groups were prepared by intermolecular oxidative coupling of dimer units or intramolecular cyclization of the corresponding open-chain oligomers. The aggregation properties were investigated by two methods, the 1H NMR spectra and the vapor pressure osmometry (VPO). Although some discrepancies were observed between the association constants obtained from the two methods, the qualitative view was consistent with each other. The analysis of self-aggregation by VPO revealed unique aggregation behavior of DBMs in acetone and toluene, which was not elucidated by the NMR method. Namely, the association constants for infinite association are several times larger than the dimerization constant, suggesting that the aggregation is enhanced by the formation of dimers (a nucleation mechanism). In polar solvents, DBMs aggregate more strongly than in chloroform due to the solvophobic interactions between the macrocyclic framework and the solvents. Moreover, DBMs self-associate in aromatic solvents such as toluene and o-xylene more readily than in chloroform. In particular, the hexameric DBM having a large macrocyclic cavity exhibits extremely large association constants in aromatic solvents. By comparing the aggregation properties of DBMs with the corresponding acyclic oligomers, the effect of the macrocyclic structure on the aggregation propensity was clarified. Finally, it turned out that DBMs tend to aggregate more readily than the corresponding phenylacetylene macrocycles, acetylene-bridged [2n]metacyclophanes, owing to the withdrawal of the electron density from the aromatic rings by the butadiyne linkages which facilitates π-π stacking interactions.
- Tobe, Yoshito,Utsumi, Naoto,Kawabata, Kazuya,Nagano, Atsushi,Adachi, Kiyomi,Araki, Shunji,Sonoda, Motohiro,Hirose, Keiji,Naemura, Koichiro
-
p. 5350 - 5364
(2007/10/03)
-