Near-Infrared fluorescent unsymmetrical aza-BODIPYs: Synthesis, photophysics and TD-DFT calculations

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 lambda(abs) the unsymmetrical aza-BODIPYs studied exhibited NIR emission with lambda(f) ranging from 699 nm to 718 nm in toluene. The fluorescence quantum yields (Phi(f)), depending on the substitution pattern, ranged from Phi(f) = 0.49 to Phi(f) = 0.22 and the fluorescence lifetimes ranged from tau(f) = 1.90 ns to tau(f) = 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. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, the synthesis and properties of four unsymmetrical aza-BODIPYs with near-infrared (NIR) fluorescence were reported. These molecules exhibited highly desirable photophysical and photochemical properties due to the presence of both strongly electron-withdrawing p-nitrophenyl rings and mildly electron-donating p-methoxyphenyl rings within the aza-BODIPY core. The unsymmetrical aza-BODIPYs showed NIR emission with wavelengths ranging from 699 nm to 718 nm, along with fluorescence quantum yields ranging from 0.22 to 0.49 and fluorescence lifetimes ranging from 1.90 ns to 3.59 ns. A specific aza-BODIPY with electron-donating and electron-withdrawing substituents at the 3 and 5 positions, respectively, was identified as a cell-permeable, NIR emitting fluorophore suitable for bioimaging.