Base-assisted one-pot synthesis of N, N ′, N ″- triaryltriazatriangulenium dyes: Enhanced fluorescence efficiency by steric constraints

Article abstract of DOI:10.1021/jo3007732

In this paper we report the first synthesis of cationic N,N′,N″-triaryltriazatriangulenium dyes (Ar₃-TATA ⁺). Previously, only alkyl-substituted triazatriangulenium derivatives (R₃-TATA⁺) were known, a consequence of the low reactivity of anilines in the aromatic nucleophilic substitution reaction leading to the formation of the TATA⁺ core. The synthesis of Ar ₃-TATA⁺ was achieved by heating the tris(2,6- dimethoxyphenyl)methylium ion (DMP₃C⁺) in various anilines in the presence of NaH. In the solvent-free reaction all three aryl substituents could be introduced despite the low reactivity of the anilines. The symmetric Ar₃-TATA⁺ derivatives with Ar = phenyl (2), 4-methoxyphenyl (3), and 4-bromophenyl (4) were synthesized. Single crystal structures of 2 and 4 were obtained as BF₄^- salts, where torsional angles larger than 80° were observed between the TATA⁺ chromophore and the aryl substituents. The photophysical properties were studied in solution and in thin films. The results show that the Ar₃- TATA⁺ dyes have a surprising 3-fold increase in fluorescence quantum yields when compared to the parent alkyl-substituted R₃-TATA ⁺ salts. With a high quantum yield (>50%) and emission in the red (_fl = 560 nm) the Ar₃-TATA⁺ dyes represent a promising new addition to the family of superstable cationic triangulenium dyes. Additionally, the synthesized tribromo derivative 4 is shown to be a potential triagonal synthon for polymers and other macromolecules.