H‐Aggregates of Oligophenyleneethynylene (OPE)‐BODIPY Systems in Water: Guest Size‐Dependent Encapsulation Mechanism and Co‐aggregate Morphology1. Issue 34 (14th July 2014)

• Record Type: Journal Article
• Authors: Allampally, Naveen Kumar; Florian, Alexander; Mayoral, María José; Rest, Christina; Stepanenko, Vladimir; Fernández, Gustavo
• Is Part Of: Chemistry. Volume 20:Issue 34(2014)
• Page Start: 10669
• Page End: 10678
• Publication Date: 2014-07-14
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201402077
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The synthesis of a new oligophenyleneethynylene (OPE)‐4, 4‐difluoro‐4‐bora‐3a, 4a‐diaza‐<italic>s</italic>‐indacene (BODIPY) bolaamphiphile <bold>1</bold> and its aqueous self‐assembly are reported. Compound <bold>1</bold> forms H‐type aggregates in aqueous and polar media, as demonstrated by UV/Vis and fluorescence experiments. Concentration‐dependent <sup>1</sup>H NMR studies in CD<sub>3</sub>CN 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 <bold>1</bold> 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 <bold>1</bold>. 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 <bold>1</bold> rigidify upon guest addition. In contrast, the co‐assembly of <bold>1</bold> 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.</p> </abstract>