Synthesis of UV absorbers based on N‑(2‑aminoaryl)benzotriazole derivatives

Through the aromatic nucleophilic substitution and reduction reactions, we obtain mixtures of 1-(2-NH2-4-CF3-phenyl)-1H- and 2-(2-NH2-4-CF3-phenyl)-2H-benzotriazoles, containing 1- and 2‑substituted isomers in various ratios. The UV absorption intensity of these amino compound mixtures was studied. All mixtures of aminobenzotriazole derivatives had absorption in the ranges of 280–200 nm, 315–280 nm, and 400–315 nm. An increase in the content of the 2‑substituted isomer in the mixture resulted in their higher ability to absorb UVA and UVB radiation. When the 1‑substituted derivative predominated in the mixture, UVC radiation was absorbed more intensely. The most promising mixture was found to be one containing the 1- and 2‑substituted isomers in a ratio of 1 : 0.49. It exhibited continuous and significant absorption over the entire studied UV spectral range. Quantum chemical calculations showed the hypsochromic shift of the absorption maxima in the UV spectrum of the 1‑substituted isomer is due to steric hindrance. It makes the molecule substantially non‑planar and disrupts the conjugation between the benzotriazole and aniline moieties. It increases both the energy gap between the HOMO and LUMO and in the energy of electronic transitions.