Preparation of Novel Porphyrin Nanomaterials Based on the pH-Responsive Shape Evolution of Porphyrin Microspheres

The shapes and properties of self-assembled materials can be adjusted easily using environmental stimuli. Yet, the stimulus-triggered shape evolution of organic microspheres in aqueous solution has rarely been reported so far. Here, a novel type of poly(allylamine hydrochloride)-g-porphyrin microspheres (PAH-g-Por MPs) was prepared by a Schiff base reaction between 2-formyl-5,10,15,20-tetraphenylporphyrin (Por-CHO) and PAH doped in 3.5-μm CaCO3 microparticles, followed by template removal. The PAH-g-Por MPs had an average diameter of 2.5 μm and could be transformed into one-dimensional nanorods (NRs) and wormlike nanostructures (WSs) after being incubated for different times in pH 1–4 HCl solutions. The rate and degree of hydrolysis had a significant effect on the formation and morphologies of the nanorods. The NRs@pH1, NRs@pH2, and NRs@pH3 were all composed of the released Por-CHO and the unhydrolyzed PAH-g-Por because of the incomplete hydrolysis of the Schiff base. However, the WSs@pH4 were formed by a pure physical shape transformation, because they had the same composition as the PAH-g-Por MPs and the Schiff base bonds were not hydrolyzed. The self-assembled NRs and WSs exhibited good colloidal stability and could emit stable red fluorescence over a relatively long period of time.