Modulating structure and properties in organic chromophores: Influence of azulene as a building block

The properties of isomeric azulene derivatives, substituted through the 5-membered ring, were examined using a combination of experimentation and theoretical calculations for a series of well-defined electroactive oligomers. The substitution pattern was shown to dramatically influence solid-state, electronic, and optical properties of the oligomers with acid-responsive materials only being observed when the azulenium cation could be directly stabilized by substituents on the 5-membered ring. In addition, the absorption maxima and optical band-gaps of the azulenium cations can be tuned by the substitution position of the azulene ring by the chromophore.