Synthesis And Application Of Far Red/Near-Infrared AIE Luminogens With Pyridine

Aggregation-Induced Emission（AIE）phenomenon is a unique photophysical phenomenon,because the fluorescence emission of propeller-like organic fluorophores after aggregation is significantly enhanced.AIE differs immensely from the generally recognized aggregation-caused emission quenching（ACQ）observed in numerous conventional organic fluorophores that own wellconjugated and planar structures.AIEgens play a significant role in the fields of bioimaging,biosensing,and anti-counterfeiting.Driven by ever-increasing interests for good applicability,fast response,excellent fluorescence and sensitivity,the novel AIEgens are prospering at an astonishing speed.Acid-base stimulus response is a phenomenon where that the ultraviolet-visible absorption and fluorescence emission spectra of organic fluorophores change significantly with the continuous change of p H.Organic fluorophores with this property are often used in the fields of acid sensors and anti-counterfeit paper.The design of the p H sensor is achieved by utilizing the protonation and deprotonation processes of the molecules.As AIEgens have unique solid-state emission properties,they play a very crucial role in acid-base stimulus response.Photodynamic therapy（PDT）is a therapy approach in which photosensitizers efficiently produce reactive oxygen species（ROS）to destroy or kill tumor cells in the presence of white light irradiation.However,the porphyrin-based photosensitizers used in clinics generally suffer from aggregation-caused reductions in the generation of emission and ROS.AIEgens,which can overcome the ACQ effect of traditional photosensitizers,cause damage to cancer cells by generating ROS under light conditions.In this work,we report a series of AIEgens with pyridine groups,which emit at the red/near-infrarad（FR/NIR）regions.Among them,the fluorophore DPP3A exhibits high solidstate FR/NIR emission with an excellent quantum yield of 48.6%.Due to the introduction of the pyridine group,the protonation/deprotonation processes of the fluorophore DPP3A were investigated.Moreover,when treated with the stimuli of HCl/NH₃vapor,the fluorophore DPP3A shows a reversible fluorescent switch between the visible(λ_em,max=652 nm)and the NIR-I region(λ_em,max=800 nm)with large emission shift and good reproducibility.Both the fluorophore DPP2A and DPP4A maintain the twisted structure,leading to the unique AIE characteristic.The fluorophore DPP4A exhibits high solid-state emission at 726 nm with an excellent quantum yield of 13.44%.Under ordinary white light irradiation,the fluorophore DPP4A has the ability to continuously produce ROS.The research results of this series of AIEgens show their potential application prospects in the fields of biosensing,anti-counterfeiting and PDT.