Chem. Commun. 2014. We demonstrate that the self-assembly in polar media and gelation of an amphiphilic Pd(II) complex with pendant chlorine ligands are governed by cooperative intra- and interstrand CHO interactions between peripheral triethylene glycol chains leading to slipped π-stacks.
Chem. Eur. J. 2014, 20. We report an innovative template-assisted synthetic protocol for the selective functionalization of terminal triple bonds in oligophenyleneethynylenes (OPE) by pre-organization in aqueous solution. By this approach, three new OPE-based bolaamphiphiles substituted with hydrophilic poly(2-ethyl-2-oxazoline) (PEtOx) chains of different length have been synthesized. The chain length was observed to strongly influence the aqueous supramolecular polymerization: bolaamphiphiles with longer hydrophilic chains aggregate into spherical nanoparticles in a stepwise fashion, whereas 2D anisotropic platelets are formed cooperatively if shorter PEtOx chains are used. Our results demonstrate that hydrophobic interactions can be strong enough to trigger cooperative effects in aqueous self-assembly processes.
Chem. Eur. J. 2014. The synthesis of a new oligophenyleneethynylene (OPE)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bolaamphiphile 1 and its aqueous self-assembly are reported. Compound 1 forms H-type aggregates in aqueous and polar media, as demonstrated by UV/Vis and fluorescence experiments. Concentration-dependent 1H NMR studies in CD3CN reveal that the BODIPY units are arranged on top of each other into π-stacks with H-type excitonic coupling, as supported by ROESY NMR and theoretical calculations and visualized by Cryo-SEM studies. A detailed analysis of the spectral changes observed in temperature-dependent UV/Vis studies reveals that 1 self-assembles in a non-cooperative (isodesmic) fashion in water. The hydrophobic interior of these self-assembled structures can be exploited to encapsulate hydrophobic dyes, such as tetracene and anthracene. Both dyes absorb in a complementary region of the UV/Vis spectrum and are small enough to interact with the hydrophobic segments of 1. Temperature-dependent UV/Vis studies reveal that the spectral changes associated to the encapsulation mechanism of tetracene can be fitted to a Boltzmann function, and the initially flexible fibres of 1 rigidify upon guest addition. In contrast, the co-assembly of 1 and anthracene is a highly cooperative process, which suggests that a different class of (more-ordered) aggregates is formed. TEM and Cryo SEM imaging show the formation of uniform spherical nanoparticles, indicating that a subtle change in the guest molecular structure induces a significant change in the encapsulation mechanism and, consequently, the aggregate morphology.
Angewandte Frontispiece: Self-Assembly and (Hydro)gelation Triggered by Cooperative π–π and Unconventional C[BOND]H⋅⋅⋅X Hydrogen Bonding Interactions†
Angew. Chem. Int. Ed., 2014. Weak C[BOND]H⋅⋅⋅X hydrogen bonds are important stabilizing forces in crystal engineering and anion recognition in solution. In contrast, their quantitative influence on the stabilization of supramolecular polymers or gels has thus far remained unexplored. Herein, we report an oligophenyleneethynylene (OPE)-based amphiphilic PtII complex that forms supramolecular polymeric structures in aqueous and polar media driven by π–π and different weak C-H⋅⋅⋅X (X=Cl, O) interactions involving chlorine atoms attached to the PtII centers as well as oxygen atoms and polarized methylene groups belonging to the peripheral glycol chains. A collection of experimental techniques (UV/Vis, 1D and 2D NMR, DLS, AFM, SEM, and X-Ray diffraction) demonstrate that the interplay between different weak noncovalent interactions leads to the cooperative formation of self-assembled structures of high aspect ratio and gels in which the molecular arrangement is maintained in the crystalline state.
J. Am. Chem. Soc., 2013, 135, 2148-2151. A new oligophenyleneethynylene (OPE)-based Pd(II) pyridyl complex has been synthesized, and its self-assembly has been investigated in solution, in the bulk state, and on surfaces. Detailed analysis of concentration- and temperature-dependent UV–vis studies in methylcyclohexane supported by DFT calculations demonstrate for the first time that cooperative supramolecular polymerization processes can be driven by metallophilic interactions.
Narcissistic versus social! G. Fernández et al. report on the self-assembly of two structurally related oligophenyleneethynylene (OPE) derivatives featuring polar or nonpolar peripheral chains and their remarkable narcissistic versus social self-sorting behaviour in aqueous media that can be controlled by concentration and solvent changes. Between 0.01 and 0.1 mm the mixture of both OPEs self-assembles into independent spherical aggregates, whereas a slight increase in concentration to 1 mm induces a co-assembly process, giving rise to large ribbon-like aggregates.
Nature Materials. 2013, 12, 12-14. Three-dimensional ordering in liquid-crystalline polymers is induced by the photopolymerization of a mixture of mesogens sandwiched between two patterned substrates. By incorporating an infrared-sensitive dye in the mixture, polymer films that undergo reversible shape deformations on heating are formed.