Cyano-substituted stilbene (CSS)-based conjugated polymers: Photophysical properties exploration and applications in photodynamic therapy

Conjugated polymers (CPs) have attracted great attention due to their excellent optical properties (such as large absorption cross section, signal amplification, high photostability etc.). As representative electron acceptors and organic small molecules which are easy to be synthesized and modified, cyano-substituted stilbene (CSS) derivatives are widely used to construct photoelectrical materials. Despite donor-acceptor (D-A) conjugated polymers based on CSS have been applied in sensing and super-resolution imaging, systematic studies about the effects of different CSS structures on the photophysical properties of CPs have rarely been reported. Therefore, we have synthesized a series of D-A conjugated polymer nanoparticles (CP NPs) based on different CSS units, and found that the photophysical properties of CP NPs including the bandgap and ΔES-T were closely associated with the structure of CSS derivatives. Moreover, the introduction of tetraphenylethylene (TPE) can relieve the aggregation-caused quenching (ACQ) effects of CSS conjugated polymers to varying degrees. The theoretical calculation further corroborated that by regulating the number and distribution of cyanide groups in the repeating units, the stronger D-A strength resulted in a redshift in the emission spectrum and the more efficient capacity of total ROS (1O2, O2•- and •OH) generation. We then selected CP6-TAT NPs, with the near infrared (NIR) emission and best ФPS, to characterize its performance in photodynamic therapy (PDT). It was revealed that CP6-TAT NPs can be regarded as an ideal candidate for PDT. The results provided a new reference for regulating the structure-effect relationship of CPs and a comprehensive method for constructing photosensitizers based on CPs.