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.