Over the past decade, it has been demonstrated that conjugated polymers can produce ROS upon irradiation with UV-visible light through spin-forbidden intersystem crossing (ISC) to sensitize the formation of singlet oxygen (¹O₂). The polymer PPET3-N2 with an alternating polyphenylene ethynylene (PPE) and terthiophene unit and quaternary ammonium side chains was synthesized by Pd-catalyzed Sonogashira coupling reaction. Compared to the PPE type of conjugated polymers, enhanced efficiency of singlet oxygen generation by PPET3–N2 was observed. Its photocytotoxicity to tumor cells has made it a potential agent for photodynamic therapy (PDT). These findings led us to explore the potential applications of this polymer in photocatalytic reactions.
Herein this work, we studied the PPET3-N2 photocatalyzed oxidation, such as oxidation of α-terpinene and selective oxidation reactions of a series of organic sulfides to form sulfoxides. These reactions were carried out with good yields and selectivity. These oxidation reactions were conducted in both bulk solution flasks and microfluidic reactors. The microfluidic reactors were able to convert reactants to desired products with higher conversion in less reaction time. For example, the microfluidic reactor may enhance the conversion of photocatalytic oxidation to over 98% within eight minutes. Different microfluidic reactors were explored and compared, including single-channel, dual-channel, and polymer-coated microreactors. This method was further applied to synthesize an antiparasitic drug to simplify the reaction conditions and improve the conversion and selectivity.

Illustration of PPET3-N2 in photocatalyzed oxidation reactions in a batch reaction system and a microfluidic reactor.

Chunyan Tan

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