Different morphologies of self-assembled nanofibers fabricated with amphiphilic low-molecular-weight azopyridinium salts

Abstract

Self-assembled nanofibers with different morphologies were successfully fabricated using amphiphilic low-molecular-weight (LMW) azopyridinium compounds having hydrophobic substituents on benzene groups. The possible driving force and self-assembly principles in nanofiber formation processes were proposed based on measurements of X-ray diffraction (XRD), UV-vis absorption spectra and polarizing optical microscopy (POM). The complicated stackings between azopyridinium salts which were constructed by three aromatic units in azopyridinium molecules, i.e. the stackings between benzene groups (Bz–Bz), pyridine groups (Py–Py) and those of benzene with pyridine groups (Bz–Py), mainly acted as the driving force for formation of LMW-AzPy nanofibers. The changed steric hindrance and hydrophobic properties of substituents on benzene groups resulted in the two aggregation types, head–tail and head–head–tail–tail, of LMW-AzPy molecules. In these cases, the head and tail are hydrophilic and hydrophobic parts of LMW-AzPys molecules, respectively. The analyses and understanding of the driving force and aggregation types of LMW-AzPy nanofibers provides references for fabrication of supramolecularly self-assembled nanofibers with controllable behaviours.