title: H-aggregates of oligophenyleneethynylene (OPE)-BODIPY systems in water: guest size-dependent encapsulation mechanism and co-aggregate morphology.
abstract: 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 (1)H 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.
authors.affiliation: Institut für Organische Chemie and Center for Nanosystems Chemistry, Universität Würzburg Am Hubland, 97074 Würzburg (Germany), Fax: (+49) 931-31-84756.
authors.forename: Naveen Kumar
authors.initials: NK
authors.lastname: Allampally
authors.forename: Alexander
authors.initials: A
authors.lastname: Florian
authors.forename: María José
authors.initials: MJ
authors.lastname: Mayoral
authors.forename: Christina
authors.initials: C
authors.lastname: Rest
authors.forename: Vladimir
authors.initials: V
authors.lastname: Stepanenko
authors.forename: Gustavo
authors.initials: G
authors.lastname: Fernández
keywords: amphiphiles; aqueous self-assembly; encapsulation; supramolecular polymerization; π-conjugated systems