A family of multi-color anthracene carboxyimides: Synthesis, spectroscopic properties, solvatochromic fluorescence and bio-imaging application

A family of anthracene carboxyimides with multi-color fluorescence have been successfully prepared, and their spectroscopic properties were investigated by UV–vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy. The photostability and solvatochromic fluorescence in organic solvents were also investigated. The parent anthracene carboxyimide 4a displays very strong green fluorescence (Φ_F = 0.91 in EtOH), good pH stability and photostability, as well as a large Stokes shift. By attachment of different substituents at the 10-position of the anthracene carboxyimide, the fluorescence maxima could be effectively modulated from 500 nm to 615 nm. The 10-(picolylamine) substituted anthracene carboxyimides 5a and 5b exhibit large Stokes shifts (>80 nm) and significant positive solvatochromic fluorescence in organic solvents due to their intramolecular charge-transfer (ICT) character. Furthermore, cell staining experiments indicate that anthracene carboxyimides have excellent cell membrane permeability and good photo-bleaching resistance in living cells. Particularly, compound 5a is a specific mitochondria-targeting dye with red fluorescence. All these features enable anthracene carboxyimides to serve as promising candidates for bio-labeling/imaging applications.