Highly Emissive Near Infrared Fluorophores Formed By Co-assembly Of Cationic/Anionic Amphiphiles:Towards Application In Cell-imaging

The development of near infrared(NIR)fluorescence imaging is expected to have significant impact on future personalized oncology owing to the very low tissue autofluorescence and high tissue penetration depth in the NIR spectrum window.To date,a variety of materials have been extensively investigated for fluorescence imaging,including fluorescent proteins,inorganic quantum dots and organic fluorescent dyes.The complex operation of fluorescent proteins and the high toxicity of inorganic quantum dots hampered their further applications.Thus,organic dyes,owing to the large variety and easy processing features,become one of the most widely studied materials.Traditional fluorescent dyes always processed the disadvantage of poor photostability,high plasma protein binding rate,and water-quenching luminescence.Therefore,the design and synthesis of NIR fluorescent dyes with excellent photophysical properties have research significance.In this work,the conjugated tetraphenylethylene and perylene bisimide were introduced as aromatic chromophore into bolaamphiphile(denoted,by PBI-TPE-11).The target molecule showed weak near infrared fluorescence emission and the peak position located at 660 nm.By co-assembly with sodium dodecyl benzene sulfonate(SDBS),the near infrared fluorescence emission of PBI-TPE-11 was greatly enhanced.Upon addition of 2-fold SDBS into the PBI-TPE-11 solution,the quantum yield was increased from 0.12%to 1.7%.Moreover,the quantum yield continues to increase when adding more SDBS,and a quantum yield as high as 12%was acquired when 140-fold of SDBS was added.By Job's Plot and Benesi-Hildebrand equation,we confirmed that the association ratio of PBI-TPE-11 and SDBS should be 1:2.Based on the results of Fourier transform infrared(FTIR)spectroscopy,we speculated the possible mechanism for the fluorescence enhancement as follow.Complexation of PBI-TPE-11 and SDBS reduced the strong ?-? stacking interaction by the alkyl chains intercalating in between the perylene bisimide groups,and thus led to the enhanced fluorescence emission.When adding more than 2-fold SDBS,the extra SDBS molecules segregated the PBI-TPE-11 molecules by surrounding them,which explains the continuous increase of quantum yield.In addition,the nanostructures formed by self-assembly of complexes were applied in labeling HeLa cells,and high contrast images were obtained.