Synthesis and properties of 2-(2-pyridyl)-1-azaazulene

The title azaazulene 3 was synthesized either by reaction of tropone with N-{(2-pyridyl)acetyl}pyridinium iodide in the presence of ammonium acetate or by palladium-catalyzed cross-coupling between 2-halo-1-azaazulene and 2-substituted pyridine. The compound shows relatively stronger basicity compared with 2,2′-bipyridyl. While 3 showed no emission from the S1 state but from the S2 state like azulene does, the protonated species of 3 exhibited emission from the S1 state. Cationic metal-dependent absorption and emission relating to complexation were also studied.