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 (f_THF = 95%) it displays strong fluorescence emission with a quantum yield of 6.33%. In the presence of spermine, emission of Su-TPE produces higher quantum yields i.e. 1 : 48 molecular ratio gives 7.21%. 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.