Porphyrin assemblies via a surfactant-assisted method: from nanospheres to nanofibers with tunable length

In this paper, we report that a porphyrin, zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), could be organized to form one-dimensional (1D) nanofibers via a surfactant-assisted self-assembly (SAS) method. We disclose that when a chloroform solution of ZnTPyP is dropwise added into an aqueous solution of cetyltrimethylammonium bromide (CTAB), spherical nanostructures are formed at the initial stage. The nanospheres are naturally transformed into 1D nanostructures simply by aging under ambient conditions. Interestingly, by adjusting the volume of the employed ZnTPyP chloroform solution, the length of thus-produced 1D nanoarchitectures could be efficiently controlled. It is disclosed that longer nanofibers could be manufactured when a small volume of chloroform solution of ZnTPyP is involved, while shorter 1D nanospecies could be produced when a large volume of chloroform solution of ZnTPyP is employed. The 1D nanostructures are characterized by UV-visible spectra, scanning electron microscopy, low-resolution transmission electron microscopy, high-resolution transmission electron microscopy, and fast Fourier transformation. A solubility experiment has been carried out to disclose the dispersibility of our ZnTPyP in plain water and in CTAB aqueous solution. On the basis of the experimental facts, an explanation is proposed for these interesting new findings. The investigation provides new opportunities for the controllable assembly of porphyrin-based 1D nanomaterials with tunable length, and it sheds new scientific insights on the molecular assembly process occurring in the SAS system, wherein an oil/water system is used as the assembly medium.