Metal-Free Nitrogen-Containing Polyheterocyclic Near-Infrared (NIR) Absorption Dyes: Synthesis, Absorption Properties, and Theoretical Calculation of Substituted 5‑Methylisoindolo[2,1‑a]quinolines

We have synthesized and theoretically calculated 5-methylisoindolo­[2,1-a]­quinoline derivatives as novel near-infrared absorption dyes via a ruthenium-catalyzed one-pot metathesis/oxidation/1,3-dipolar cycloaddition protocol. The reactivity in 1,3-dipolar cycloaddition was governed by the electronic effect of aromatic ring substituents. Substrates with an electron-withdrawing group on the aromatic ring afforded higher yields. The maximal absorption wavelength of 3,5-dimethyl-11-phenylisoindolo­[2,1-a]­quinoline-7,10-dione and 11-(4-methoxyphenyl)-5-methylisoindolo­[2,1-a]­quinoline-7,10-dione in MeOH increased to 736 and 737 nm, although that of 3a was 727 nm.