Non-amphiphilic pyrene cored poly(aryl ether) dendron based gels: tunable morphology, unusual solvent effects on the emission and fluoride ion detection by the self-assembled superstructures

The design, synthesis and study of morphology as well as photophysical properties of novel low molecular weight gels (LMWG) based on non-amphiphilic pyrene cored poly(aryl ether) dendron derivatives are described. Solvent controlled self-assembly in the system results in nano-sized vesicles, which further aggregate to micro-sized vesicles and finally turned to entangled fibrillar type arrangement in the gel phase. The morphology transformations were investigated by dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (LSCM) experiments. The nano-/micro-sized vesicles and fibre aggregates exhibit an intense light emitting property from the pyrene moiety, which is attached to the dendron through an acylhydrazone spacer group. More interestingly, the luminescence properties were found to be controlled by the solvent polarity, in a rather unusual manner, due to the selective formation of pyrene ‘excimer’ and ‘exciplex’ in solvent controlled aggregates. Furthermore, the system has been utilized to detect fluoride ions through a reversible gel–sol transition, which is associated with a color change from yellow to red.