Multifunctional materials that simultaneously provide therapeutic action and image the results provide new strategies for the treatment of various diseases. Here, it is shown that water soluble conjugated polymers with a molecular design centered on the polythiophene-porphyrin dyad are effective for killing neighboring cells. Following photoexcitation, energy is efficiently transferred from the polythiophene backbone to the porphyrin units, which readily produce singlet oxygen ((1)O(2)) that is toxic for the cells. Due to the light-harvesting ability of the electronically delocalized backbone and the efficient energy transfer amongst optical partners, the polythiophene-porphyrin dyad shows a higher (1)O(2) generation efficiency than a small molecule analog. The fluorescent properties of these polymers can also serve to distinguish amongst living and dead cells. Polymers can be designed with folic acid grafted onto the polymer side chain that can specifically kill folate receptor-overexpressed cells, thereby providing an important demonstration of anticancer specificity through molecular design.