Achieving beyond 100% Triplet State Generation with Singlet Fission Strategy for High-Performance Photosensitizer Design

As the key of photodynamic therapy (PDT), the current photosensitizer (PS) design highly relies on promoting the intersystem crossing (ISC) process to form the triplet excited state, thus generating toxic reactive oxygen species (ROS). However, ISC is a spin-forbidden process with a low triplet state generation yield (<100%). Herein, as a proof of concept, we report a new strategy of aggregation induced singlet fission (SF) process with an ultrafast rate (<100 ps) and a very high triplet yield (>100%) to design efficient PSs. Such a unique SF strategy is demonstrated with an anthracene derivative of BPA-An, which shows J-aggregation enhanced ROS generation ability. Mechanism studies with aggregation behavior and fs-transient absorption spectroscopy indicate that BPA-An in J-aggregate state can efficiently generate triplet state via the SF process with a 158% triplet yield and thus possesses excellent Type-I and Type-II ROS generation ability in nanoparticle (NP) format. Both cellular and animal experiments further prove the excellent PDT antitumor performance of BPA-An NPs. To the best of our knowledge, this work shall represent the first example of utilizing SF as the design rule to promote the triplet state generation of PSs, which shall pave a new avenue in PDT.