Homocoupling-Defect-Free Alternating Conjugated Polymers With Enhanced Photosensitization for Phototherapy

Defects are inevitably introduced to the materials during the synthesis or preparation process, and sometimes bring out huge effects on the performance. Conjugated polymers, especially the donor-acceptor alternating ones, have been termed as good candidates in phototherapy, since their strong light-harvesting ability and increased intersystem crossing channels from singlet to triplet states could improve the reactive oxygen species (ROS) generation efficiency. Such alternating conjugated polymers are usually prepared though Stille or Suzuki cross-coupling polymerization between two types monomers of donor and acceptor, which in fact usually results in homocoupling defect of donor-donor or acceptor-acceptor structures in obtained polymers. In this contribution, we prepared a series of donor-acceptor-type alternating conjugated polymers photosensitizers through different polymerization processes, and found that all the polymers prepared by direct arylation coupling polymerization (DArP) showed much better ROS generation efficiencies and fluorescence intensities than their similar analogues prepared by Suzuki polymerization. Detailed mechanism studies confirmed that the donor-donor or acceptor-acceptor defects could decrease the exciton lifetimes of the donor-acceptor alternating polymers upon laser irradiation through obstructing exciton diffusion, and the homocoupling-defect-free polymers prepared by DArP therefore demonstrated better performance. In addition, PTD-DArP, constructed by triphenylamine donor and diketopyrrolopyrrole acceptor, demonstrated much better biodegradation capacity than PTD-Suzuki, and it could also match the 660 nm clinical laser, making it good candidate in phototherapy, which has been further confirmed by both in vitro and in vivo results via two models of tumor and diabetes infection. At last, by using two previously reported high performance conjugated polymer photosensitizers as the models, the universality of our strategy was further verified.