Impact of 2,6-connectivity in azulene: optical properties and stimuli responsive behavior

Abstract

The possible incorporation of the redox active, small donor acceptor molecule azulene as a core structure for potential optoelectronic applications has been evaluated. The synthesis and characterization of different isomers of di(phenylethynyl)azulene 1–4 have been successfully carried out. The photophysical properties as well as their stimuli responsive behavior reflecting their corresponding electronic properties were also investigated. The experimental observations show that 2,6-connection (3) exhibits intense luminescence and shows the strongest stimuli responsive behavior upon acid treatment. DFT calculations of 3 reveal the highest contributions of the alkyne substituents at the 2- and 6-position of the azulene to the ground- and excited state that makes the 2,6-connectivity at azulene a very promising candidate for low band-gap conjugated materials.