Spectroelectrochemical characterization of isomeric conjugated polymers containing 2,7- and 3,6-carbazole linked by vinylene and ethynylene segments

Abstract

The ability to form multi-colored oxidation states upon applied positive potentials, and the narrow band gap of 2,7-substituted carbazole derivatives, had encouraged the development of new carbazole containing polymers with interesting optoelectronic properties. Four conjugated polymers containing substituted carbazole units spaced in the main chain by vinylene and 1,4-phenyleneethynylene segments were synthesized via Stille and Sonogashira coupling reactions. Two different substitution positions of carbazole, such as 2,7- and 3,6-carbazole were used to tune the conjugation length and the charge transfer properties of the resulting polymers. The structures of the obtained polymers were characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy while the electronic and optical properties were investigated as function of carbazole substitution positions or spacer nature by ultraviolet-visible spectroscopy and cyclic voltammetry. The redox behaviour of polymers as films deposited on working electrode was investigated using cyclic voltammetry technique, and the lowest unoccupied molecular orbital and highest unoccupied molecular orbital energy levels values were also determined. Spectroelectrochemical measurements suggested the existence of polaronic and bipolaronic structures of polymers backbones accompanied by multi-electrochromic behavior.