Impact of Naphthalimide-Fusion Positions on Properties of Azulene Derivatives

Abstract

In the Suzuki–Miyaura–Heck condensation reaction of 1-borylazulene with 4,5-dibromo-1,8-naphthalimide, we found the formation of naphthalimide-fused azulene at 1,8-positions (1,8-NIA) in 49% yield and an unexpected 1,2-fused product (1,2-NIA) in 6% yield, respectively. 1,2-NIA involves a pentalene skeleton at the central part and was characterized using NMR and single-crystal X-ray analysis. The condensation positions significantly affect their UV–vis–NIR absorption spectra: the absorption maximum of 1,8-NIA is 862 nm longer than that of 1,2-NIA (739 nm). TD-DFT calculations were performed to elucidate these electronic structures and revealed the effective π-elongation strategy.