Spermine-directed supramolecular self-assembly of water-soluble AIE-active tetraphenylethylene: nanobelt, nanosheet, globular and nanotubular structures

Abstract

Tetrasulfonate-tetraphenylethylene (Su-TPE) is non-emissive in water and upon addition of a good solvent such as THF (fTHF = 95 percent) it displays strong fluorescence emission with a quantum yield of 6.33 percent. In the presence of spermine, emission of Su-TPE produces higher quantum yields i.e. 1:48 molecular ratio gives 7.21 percent. Furthermore, interaction of spermine with Su-TPE is also shown to be pH dependent. Scanning electron microscopy (SEM) of Su-TPE molecule self-assemblies demonstrates that it produces various supramolecular structures at different Su-TPE:spermine molecular ratios. Nanobelts were obtained at 1:12, evolving into microsheets at 1:24, microglobular morphology at 1:36 and microtubes at 1:48 molecular ratios, respectively. Additionally, enhanced fluorescence emission was observed upon increasing the molar ratio of spermine with Su-TPE at pH 7. The physical characterisation of the system was performed using dynamic light scattering and zeta potential measurements.