Fig. 1. Working mechanism of PSs described by the Jablonski diagram, as well as some strategies for improving their metabolism or degradability

Fig. 2. PSs containing PEG chains. (a) Preparation of Pa‐PEG NPs^[47]; (b) biodistribution of Pa‐PEG NPs in major organs over time^[47]; (c) variation trend of tumor volume with days in mice under different treatment groups^[47]; (d) tumor mass of mice in different treatment groups after 14 days^[47]; (e) structure, molar mass, and hydrodynamic diameter of 800CW-PEGn^[48]; (f) fluorescence imaging of mice injected with 800CW and 800CW-PEG45 intravenously within 30 min^[48]; (g) relationship between the molecular mass of 800CW-PEGn and RCE after 2 h intravenous injection^[48]

Fig. 3. BODIPY based PSs with both hydrophilic chains and positive charges^[49]. (a) Chemical structures of 1a‒4a; (b) size distributions of 1a‒3a NPs; (c) Zeta potential values of 1a‒3a NPs; (d) electron paramagnetic resonance results of 1a; (e) intracellular ROS imaging of 1a in cancer cells; (f) imaging of 1a in different types of cancer cells and healthy cells; (g) biodistribution of 1a in various organs after intravenous injection for different time; (h) cumulative clearance of 1a and 3a in the urine determined by fluorescence intensity; (i) percentage of injected dose of 1a and 3a in plasma over time determined by fluorescence intensity

Fig. 4. Phthalocyanine based PSs with morpholine moieties^[50]. (a) Chemical structure and self-assembly of PcSZ; (b) size distribution of NanoPcSZ; (c) fluorescence imaging of various organs after injection of NanoPcSZ for 2 and 24 h or NanoPcSZ with 1% Cremophor EL for 24 h; (d) fluorescence signals of urine and feces of mice after injection with NanoPcSZ for different time; (e) fluorescence imaging of mice urine after injection with NanoPcSZ for different time

Fig. 5. PSs containing easily oxidizable moieties. (a) Chemical structure of FBD, as well as its oxidation and subsequent metabolism process; (b) real time fluorescence imaging of tumor bearing mice after intravenous injection of FBD^[53]; (c) preparation of BP, ZnBP, BPL, ZnBPL, and ZnBPLD; (d) ROS generation efficiency of ZnBPL(w), ZnBP(w), and ZnBPD(w)^[54]; (e) photocytotoxicity of ZnBPL(w), ZnBP(w), and ZnBPD(w) against HeLa cells^[54]; (f) in vivo relative fluorescence intensity changes of different PSs after light irradiation for different time^[54]; (g) pharmacokinetics study of ZnBPL(w) under different conditions^[54]

Fig. 6. Degradable supramolecular PSs^[55]. (a) Chemical structures of BDP2IPh and BDP2IPh-CB[7], as well as the degradation of BDP2IPh-CB[7]; (b) the triplet state lifetime of BDP2IPh in ultrapure water; (c) the triplet state lifetime of BDP2IPh-CB[7] in ultrapure water; (d) ROS generation ability of BDP2IPh and BDP2IPh-CB[7] measured by using DCFH as the indicator; (e) cyclic voltammetry test results of BDP2IPh and BDP2IPh-CB[7]; (f) photobleaching of BDP2IPh and BDP2IPh-CB[7]; (g) MCF-7 cell viability of BDP2IPh and BDP2IPh-CB[7] under dark

Fig. 7. Conjugated polymer PSs with methyl imidazole as degradable moieties. (a) Chemical structure and degradation mechanism of CP1^[57]; (b) chemical structure of CP⁺, as well as the preparation of CP⁺ and CP⁺- CpG NPs^[58]

Fig. 8. PSs with anthracene as the degradation moieties^[59]. (a) Chemical structure and degradation mechanism of TPA-An-Py; (b) size distribution analysis and the transmission electron microscopy image (inset photo) of TPA-An-Py NPs; (c) absorption spectra of TPA-An-Py after light irradiation for different time; (d) relative ¹O₂ production capacity before and after 10 min white light pretreatment of TPA-An-Py; (e) intracellular ROS production capacity of different PSs; (f) confocal laser scanning microscopy images of CAM/PI-stained 4T1 cells incubated with TPA-An-Py NPs or TPA-Py NPs under different conditions

Fig. 9. Self-immolative degradable PSs^[60]. (a) Chemical structure of NG-cRGD, as well as its degradation process; (b) morphology changes of HeLa cells after treatment with 10 μmol/L PS in the presence or absence of light for 60 s; (c) mitochondria and endoplasmic reticulum swelling in HeLa cells treated with 10 μmol/L PS in the presence or absence of light for 60 s; (d)(e) in vivo fluorescence imaging and fluorescence intensity at tumor site of A549-bearing mice intravenously injected with NG-cRGD (2 mg/kg) at indicated time; (f) changes in fluorescence intensity at 710 nm and 620 nm before and after light irradiation

Fig. 10. Conjugated polymer PSs with DPP as the degradable moieties. (a) Chemical structure of DTT, as well as preparation and degradation mechanism of p-DTT NPs^[64]; (b) chemical structures of PTD-C8, PTD-C12, PTD-C16, and PTD-C20^[65]

Fig. 11. Conjugated polymer PSs with DPP and double bonds as the degradable moieties^[66]. (a) Chemical structure of BSPN, as well as the preparation of their corresponding NPs; (b) fluorescence of BSPN 50 in 450‒750 nm upon HClO treatment for different time; (c) fluorescence intensity changes of BSPN at 525 nm upon HClO treatment for different time; (d) fluorescence spectra of BSPN 50 in 450‒600 nm upon treatment of H₂O₂ and MPO at 37 ℃ for different time in PBS buffer containing NaCl; (e) fluorescence intensity changes of BSPN at 525 nm upon treatment of H₂O₂ and MPO for different time; (f) confocal fluorescence images of M1 type RAW264.7 cells incubated with BSPN 50 or BSPN 100 for 0, 12 and 24 h; (g) PA images of mice after intravenous injection with BSPN 50 or BSPN 100 for different time, where the red circles indicate the position of liver; (h) tumor volume changes of 4T1 xenografted mice versus post-treatment time under different treatments; (i) body weight of 4T1 xenografted mice versus post-treatment time under different treatments; (j) image of tumors resected from mice after different treatments for 14 d

Fig. 12. Degradable PSs with dual degradation modes^[67]. (a) Chemical structure and degradation mechanism of SQSe; (b) changes of absorption spectra of SQSe upon light irradiation for different time; (c) FT-IR spectra of SQSe before and after light irradiation for 10 min; (d) changes of absorbance of SQSe in the individual presence of •OH or H₂O₂ or O₂^•- or ¹O₂; (e) time-dependent fluorescence images of tumor bearing mice after intratumoral injection of SQSe with or without irradiation; (f) digital photographs of the right rear paws from the mice in PBS, Ce6, and SQSe groups after indoor light exposure post PDT, as well as H&E staining of the claw and partial enlargement images

Fig. 13. Degradable pseudo conjugated polymer PSs^[71]. (a) Chemical structures of PSP^Bodipy and its corresponding monomers; (b) CLSM images showing intracellular ROS generation results in 143B cells after various treatments; (c) flow cytometry images showing intracellular ROS generation results in 143B cells after various treatments; (d) survival rate of 143B and K7M2 cells with various treatments for 24 h