Synthesis and optical properties of 1-ethyl-indol-3-yl-substituted aza-BODIPY dyes at the 1,7-positions

Abstract New aza-BODIPYs with significant bathochromic shifts in their UV-vis absorption spectrum were synthesized by the installation of 1-ethyl-indol-3-yl moieties at the 1,7-positions of the aza-BODIPY core bearing 4-substituted phenyl or thien-2-yl groups at the 3,5-positions. The compounds described herein show strong NIR absorptions up to 779 nm, and emissions up to 805 nm in chloroform solution, and present large molar extinction coefficients. The absorption and emission bands of aza–BODIPYs were significantly red-shifted, by ca 100 nm, relative to the 3,5-dianisyl-1,7-diphenyl aza-BODIPY. TD-DFT calculations indicate an effective electronic conjugation between the aza-BODIPY core and the substituents. Absorption of the studied aza-BODIPY derivatives corresponds to a charge transfer from donor substituents toward the boron-centered core. Moreover, computational results show that all the compounds present HOMO–LUMO band gap values that are in the organic semiconductor range.