Controlling the self-assembly and photophysical properties of biscyanovinyl terphenyl-based hexacatenars by changing the degree of fluorination

Abstract

ABSTRACT Four series of biscyanovinyl terphenyl-based hexacatenars in which the central core was fluorinated with different number of fluorine atoms were synthesised using Suzuki and Knoevenagel reactions. The influence of the degree of fluorination on the self-assembly behaviours and photophysical properties was investigated by polarising optical microscopy (POM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), SEM, UV-vis spectroscopy and photoluminescence measurements in detail. The non-, mono- and bi- fluoro compounds could only form columnar mesophase, whereas tetra-fluoro compounds were non-mesogens. The degree of fluorination had a great effect on the gelation and morphology transition. Theoretical calculations reveal that the lower degree of fluorination has little influence on the electron density distributions of the HOMO and LUMO, whereas an opposite phenomenon was observed in the highest fluorinated compounds, indicating that stronger intermolecular interactions could be achieved by increasing the degree of fluorination. Tetra-fluoro compounds displayed stronger solvatochromism than that of the other compounds due to intramolecular charge transfer (ICT) resulted from more fluorine atoms. Additionally, all these hexacatenars show AIE behaviours. These observations indicated that tuning the degree of fluorination could change the self-assembly nanostructures and photophysical behaviours which pave a new pathway to develop sophisticated multifunctional materials.