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

Abstract

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.