Soluble Variable Color Carbazole-Containing Electrochromic Polymers

Three new carbazole-containing polymers were synthesized through Suzuki cross-coupling between N-octylearbazole-3,6-bis(ethyleneboronate) (NOctCz(BO2Et)(2)) and several arylene dibromides. 2,5-Dibromothiophene (DBT), 2,2'-dibromo-5,5'-bithiophene (DBBT), and 4,7-dibromo-2,1,3-benzothiadiazole (DBBTD) gave the three polymers PCzTh, PCzBi, and PCzBTD, respectively. Cyclic voltammetry showed two separate redox processes for each polymer, PCzTh (E-1/2 = 0.33 V and E-1/2 = 0.65 V vs Fc/Fc(+)), PCzBi (E-1/2 = 0.32 V and E-1/2 = 0.60 V vs Fc/Fc(+)), and PCzBTD (E-1/2 = 0.56 V and E-1/2 = 0.84 V vs Fc/Fc(+)). The two redox couples signify the presence of stable radical cation and dication oxidation states. In addition, the three materials were observed to display electrochromic properties. UV/vis/NIR absorbance spectroscopy revealed that each of the polymers displayed a unique absorbance maximum (345 nm for PCzTh, 375 nm for PCzBi, and 460 nm for PCzBTD) in their neutral states. Spectroelectrochemical analyses demonstrated that the pi to pi* transition was depleted upon application of increasingly positive potentials, giving rise to color changes. The different color states were quantified by colorimetry. PCzTh exhibits a yellow neutral state, a faint green radical cation state, and a pink dication state. PCzBi is yellow in its neutral state, light orange as a radical cation, and gray when fully oxidized. PCzBTD is orange when neutral, green-gray at intermediate potentials, and slate-gray as a dication.