In view of the ever-growing demand for efficient NIR fluorophores for biomedical applications, we herein report the synthesis and properties of four unsymmetrical aza-BODIPYs exhibiting NIR fluorescence. Highly desirable photophysical and photochemical properties were induced in these molecules due to the presence of both strongly electron-withdrawing p-nitrophenyl rings (p-NO2Ph-) and mildly electron-donating p-methoxyphenyl rings (p-MeOPh-) within the aza-BODIPY core. In particular, upon excitation with λabs the unsymmetrical aza-BODIPYs studied exhibited NIR emission with λf ranging from 699 nm to 718 nm in toluene. The fluorescence quantum yields (Φf), depending on the substitution pattern, ranged from Φf = 0.49 to Φf = 0.22 and the fluorescence lifetimes ranged from τf = 1.90 ns to τf = 3.59 ns. Aza-BODIPY with electron-donating substituent at 3 position and electron-withdrawing substituent at 5 position was identified as cell permeable, NIR emitting fluorophore suitable for bioimaging.
Keywords: Aza-BODIPYs; Bioimaging; Donor-acceptor systems; Dyes/Pigments; NIR fluorescence.
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