The photochemistry of poly{p-phenylene[1-(tetrahydrothiophen-1-io)ethylene chloride]} (PPTEC), a water soluble precursor of the semiconducting polymer, poly{p-phenylenevinylene} (PPV), has been studied both under atmospheric conditions and in environments devoid of oxygen. UV-visible spectroscopy and photoluminescence data has been used to provide a picture of the mechanistic pathways involved in UV irradiation of the PPTEC material. A new quantitative model for the effect of UV irradiation upon film morphology is presented, which leads to insights for the improved control of the characteristics of PPV nanostructures produced via near-field scanning optical lithography.