High brightness NIR luminescence BOPYINs: Synthesis, optical properties, acidic and viscosity response

Abstract

To obtain dyes exhibiting NIR emission and maintaining highly fluorescence quantum yield (FQY), a novel series of BO-DEs featuring a D-π-A system were synthesized starting from BOPYINs with visible emission in this work. BO-DEs with maximum emission wavelength ranging from 700 to 824 nm in solvents with different polarity. Compared to the previous work, the addition of a double bond on the π-bridge of BO-DE-1 led to a significant red shift with ca. 100 nm in variety of solvents vs that of YD6. Moreover, the introduction of a cyano group onto indole unit endows BO-DE-4 with emission peak at 794 nm and a relatively strong FQY of 7.8 % in DCM. Additionally, the AIE effect and acidic/viscosity response are detected in BO-DEs. Furthermore, the structure of BO-DE-1 were further demonstrated by single-crystal, and optical properties of BO-DEs were discussed through DFT calculations. This work provides an effective pathway for the preparation of high brightness NIR emission dyes based on BOPYINs, which is meaningful for fluorescence imaging in vivo.