Photosensitized Solid-state Polymerization of Diacetylenes in Nanoporous TiO2 Structures

In situ topochemical polymerization of two diacetylene monomers within nanoporous TiO2 thin films was carried out under visible light irradiation. One of the monomers used contains a carboxylic acid group, which could help to link the monomer onto the TiO2 surface covalently. UV-Vis absorption and Raman studies showed that both monomers were successfully photopolymerized. These results suggest that the covalent linkage of the diacetylene to the nanoparticle through the carboxylic acid group is not needed. Since photopolymerization of diacetylene is typically induced by excitation of the monomer at 300 nm, the observed red shift of the photopolymerization wavelength is attributed to the photosensitization effect of TiO2. The morphological study of the polydiacetylene/TiO2 nanocomposite revealed that the diacetylene monomers were polymerized in the vicinity of the TiO2 nanoparticles. This is attributed to the fact that the electron-transfer process occurs at the interface of nanocrystalline TiO2 (nc-TiO2) and the diacetylene monomer and the polymerization is expected to be initiated near the nc-TiO2 surface. Photopolymerization of the carboxylated diacetylene monomer with other oxides nanoparticles, such as ZnO and SiO2 was also investigated.