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A series of poly(phenylenevinylene) (PPV)/titanium oxide (TiO2) nanocompositeswith different contents of TiO2 nanoparticles were prepared from mixtures of PPVprecursor and titanium butoxide ethanol solution in a sol-gel process. TEM imagesshowed the formation of the connected network of TiO2 nanoparticles with a highercontent of TiO2, which resulted in the titanium butoxide hydrolyzed to form Ti organiccompound. Meanwhile, the conjugation of PPV polymer chains can be interrupted bythe TiO2 network structure. The PL spectra revealed that the emitted light of thePPV/TiO2 nanocomposites blue shifted without fine structure and the PL intensityenhanced when the TiO2 network formed. In the lifetime spectroscopy of positronannihilation, the structural properties of the PPV dominated the character of thenanocomposites, in which the formation of the o-Ps was presented in free volume pfpolymer, when the content of TiO2 was below 10%. Further increasing the contentof TiO2 nanoparticle introduced much more vacancies, vacancy clusters and grainboundaries at their interfaces, which led to the corresponding lifetime and intensityclose to that of the nano-TiO2 bulk materials. With the TiO2 content of 50%, theholes formed by aggregating vacancy clusters and increased the component of longlifetime. These phenomena suggested that the optical and structural properties of thePPV/TiO2 nanocomposites are dependent on the interfacial structure between PPVand TiO2 nanoparticles.