Rational design of near-infrared platinum(ii)-acetylide conjugated polymers for photoacoustic imaging-guided synergistic phototherapy under 808 nm irradiation

The preferable photoconversion tunability of conjugated polymers (CPs) is of great interest in cancer phototherapy. However, very few molecular design strategies have been developed for achieving CPs with highly efficient photoconversion performance. Herein, a rational design of near-infrared (NIR) Pt-acetylide conjugated polymer CP3 with highly efficient photoconversion behaviors for synergistic photodynamic therapy (PDT) and photothermal therapy (PTT) was demonstrated. CP3 containing boron dipyrromethene (BDP) units displayed intense absorption peaks in the NIR region, which were red-shifted approximately 60 nm compared to the corresponding small-molecule precursor of BDP. Compared with control polymers CP1 and CP2, after the introduction of Pt into CP3, the triplet state, which benefits the generation of reactive oxygen species for photodynamic therapy, was identified clearly in both CP3 and the prepared CP3 nanoparticles (CP3-NPs) by ultrafast femtosecond transient absorption (fs-TA) spectroscopy. Notably, different from the traditional nonradiative decay channel with lifetime of 1.1 ps in CP3, CP3-NPs possess an additional nonradiative decay channel with lifetime of 10 ps, both of which contribute to the superior photothermal conversion effect upon 808 nm irrradiation. All these photoconversion performances lead to excellent tumor ablation. This study elucidates the excited-state dynamics in Pt-acetylide CPs, which provide an insightful understanding and valuable guidelines for the future design of high-performance theranostic agents based on CPs for synergistic cancer phototherapy.