Self-Assembly of a Perfluorinated Amphiphilic Cyanine Dye into Branched Tubular J-Aggregates

The self-assembly process is governed by the individual constituents of molecules through precise non-covalent interactions. Amphiphilic cyanines are intriguing in supramolecular chemistry due to the large polarizability of their delocalized π-electron systems, their tuneable optical properties and their ability to form well-defined self-assembled structures in different media. Here we present the synthesis of a novel tetrahydroxy amphiphilic carbocyanine dye with perfluoro alkylated chains -(CH₂)₂-(CF₂)₅-CF₃ as hydrophobic segments and aminoproanediol as hydrophilic segment. The target molecule was synthesized in a multi-step process, which illustrates the complexity and precision required to achieve the desired structure. This study focuses on the comparison of the influence of C₈H₁₇ and C₈H₄F₁₃ tails and the effects of carboxylated and non-ionic aminopropanediol head groups as substituents on self-assembly of the TBC dye. Absorption and fluorescence measurements show similar spectroscopic properties to cyanine dyes studied previously. Cryogenic transmission electron microscopy (cryo-TEM) reveals formation of multiple supramolecular aggregates. As supramolecular assembly is very sensitive to sample preparation, multilamellar or multivesicular vesicles are obtained preferentially in vigorously vortexed solutions. Moreover, time-dependent tube formation was observed in gently mixed solutions. Thereby, we could follow the growing mechanism of the unprecedented Y-junctions of supramolecular tubes.