Electrochemistry and near-infrared electrochromism of electropolymerized polydithiophenes with β, β′-Positions bridged by carbonyl or dicarbonyl substitute

The β, β′-positions carbonyl or dicarbonyl bridged dithiophenes were prepared and electrochemically polymerized into corresponding polymers, polycyclopenta[2,1-b;3,4-b′]dithiophen-4-one (PCDK) or polybenzo[1,2-b:6,5-b′]dithiophene-4,5-dione (PCD2K), in boron trifluoride diethyl etherate based electrolyte. Potentiostatic and potentiodynamic methods confirmed that the PCDK and PCD2K films can be successfully electrodeposited in high quality with comparable intermolecular spacings at around 3.1 Å-3.2 Å. The mass changes and ion transport of the two polymers during redox processes were studied by electrochemical quartz crystal microbalance and in situ spectroelectrochemical methods, to investigate the formation of the two polymers. In situ UV-visible spectroscopy evidenced the PCDK and PCD2K evolved into polarons in the near infrared region under applied potentials. Electrochromic behaviors showed that the PCDK film appeared reddish brown in neutral state and cyan or green in oxidized state while the PCD2K showed green to dark green from neutral to oxidized states. Potential switching between oxidized and neutral states of the two films revealed that maxima transmittance changes were 38.23% and 36.64% for the PCDK and PCD2K. Thermal degradation of the two polymers showed their robust stability that allows for the application in a wide temperature scale. © 2014 Elsevier Ltd. All rights reserved.