Base-Assisted One-Pot Synthesis of N,N′,N″-Triaryltriazatriangulenium Dyes: Enhanced Fluorescence Efficiency by Steric Constraints

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 Ar3-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 (λfl = 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.