Synthesis of Triazabenzo[a]pyrenes and Their Photophysical, Acid‐Responsive, and Electrochemical Properties.

A series of triazabenzo[a]pyrenes comprising a cata‐condensed pyridine ring and 4,10‐diazapyrene framework were synthesized from commercially available materials in the following three steps: palladium‐catalyzed direct C−H arylation, nucleophilic addition of Grignard reagents to cyano groups, and copper‐catalyzed oxidative C−N bond formation. The triazabenzo[a]pyrenes showed superior electron‐accepting properties and narrower HOMO‐LUMO energy gaps compared to the corresponding 4,10‐diazapyrene derivative because of the condensation of an electron‐deficient pyridine ring. The photophysical, acid‐responsive, and electrochemical properties of triazabenzo[a]pyrenes depend on the position of the nitrogen atom in the cata‐condensed pyridine ring. Density functional theory calculations revel that the condensation of a pyridine ring leads to a lowering of the LUMO energy level thereby enhancing the electron‐accepting properties. [ABSTRACT FROM AUTHOR]