Stereochemistry controlled supramolecular architectures of novel tetrahydroxy functionalized amphiphilic carbocyanine dye

The synthesis of novel amphiphilic 5,5',6,6'-tetrachloro-benzimidacarbocyanine (TBC) dye derivatives with amino-propanediol head groups is reported, which only differ in stereochemistry (chiral enantiomers, meso-form, and conformer). For the achiral meso-form, a new synthetic route towards asymmetric cyanine dyes was established. All compounds form J-aggregates in water whose optical properties were characterized by spectroscopic methods. The supramolecular structure of the aggregates was investigated by cryo-transmission electron microscopy (cryo-TEM), cryo-electron tomo-graphy (cryo-ET), and atomic force microscopy (AFM) revealing extended sheet-like aggregates for the chiral enantiomers and nanotubes for the mesomer, respectively, while the conformer forms predominately needle-like crystals. The experiments demonstrate that the aggregation behavior of compounds can be controlled solely by head group stereochemistry which in case of the enantiomers enables formation of extended hydrogen bond chains by the hydroxyl functionalities. In case of the achiral meso-form, however, such chains turned out to be sterically excluded.