Incorporation of 1,3-Free-2,6-Connected Azulene Units into the Backbone of Conjugated Polymers: Improving Proton Responsiveness and Electrical Conductivity.

Azulene as a potential building block for constructing organic/polymeric conjugated materials has attracted more and more attention due to its unique chemical structure and physicochemical properties. However, up to now, most reported azulene-based conjugated polymers have been dominated by the connection of the five-membered ring of azulene through 1,3-positions. Herein, by incorporating 1,3-free-2,6-connected azulene units into the polymeric backbone, two azulene-based all-carbon conjugated polymers P1 and P2 with different connection ways of 2,6-azulene and 2,7-fluorene units were presented. Protonation of these two polymers with trifluoroacetic acid leads to rapid and reversible color changes in both the solution and thin-film state. Moreover, these 1,3-free-2,6-connected azulene-based conjugated polymers exhibit high electrical conductivity (2.94 and 0.32 S/cm for P1 and P2 , respectively) in thin film when doped by trifluoromethanesulfonic acid.