Stimuli-Responsive Azulene-Based Conjugated Small Molecules and Polymers with Polyaniline-like Properties.

Elizabeth Amir, Polymer and Plastics Engineering, Shenkar College, Ramat Gan, Israel

Functional materials with optical, conductive, and electron-transfer properties are gaining increasing importance in light of their application in electronic and luminescent devices. As a distinct subset, stimuli-responsive conjugated polymers incorporating electroactive units as substituents or as part of the polymer backbone have received attention with a focus on the construction of molecular based devices such as molecular wires and electrogenic sensors. Azulenes, which show unique photophysical and redox properties derived from their unusual dipolar and π-electron polarization, represent ideal building blocks for these stimuli-responsive systems.

We have obtained an access to the oligoazulene-based materials conjugated with various aromatic chromophores through the seven-membered ring of azulene. This non-traditional connectivity results in distinctive solid-state organization and electrochemical behavior when compared with isomeric azulene derivatives having the standard five-membered ring substitution pattern. In a reversible process, the optical band gap of these oligoazulenes could easily be modulated by simple protonation, with fluorescence being “switched on” upon generation of the corresponding azulenium cations. The presence of the aromatic units is effective for the generation and stabilization of azulenium cations, and the modularity of our regiospecific approach allows tuning the absorption maximum and optical bandgap of the azulenium cations by the nature of the substituents. In addition, this talk will describe synthesis of a new family of stimuli-responsible polyazulenes connected through the seven-membered ring by Yamamoto-, Sonogashira-, and Stille-coupling of 4,7-dibromoazulenes. The degree of conjugation of the polymer backbone and the reversibility of optical properties upon protonation and deprotonation is sensitive to the steric environment of the seven- membered ring and can be tuned by both substitution and incorporation of linkers between the azulene units.

Papers:

E. Amir, et al. J. Am. Chem. Soc., 2011, 133, 10046-10049.
E. Amir, et al. Chem. Sci., 2012, 3, 2721-2725.
E. Amir, et al. Chem. Sci., 2014, 5, 4483-4489.