Dual-polymer electrochromic film characterization using bipotentiostatic control

We report an analytical method which allows the systematic variation of color states of pairs of electrochromic conjugated conducting polymers with simultaneous spectroelectrochemical and colorimetric characterization of the resulting color summation. This method measures colors by transmitting light through two polymer films stacked together in electrolyte and under separate potentiostatic control. The polymers that were used in this work are poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-propylenedioxypyrrole) (PProDOP), and dihexyl substituted poly(3,4-propylenedioxythiophene) (PProDOT-Hx2). These are all cathodically coloring polymers, PEDOT switching from a transmissive sky blue to a deep blue, PProDOP switching from a highly transmissive gray/blue to a brown and then to an orange, and PProDOT-Hx2 switching from a transmissive sky blue to a deep blue-purple color upon reduction. Coupling these polymers logically by the dual-polymer electrochromic film characterization technique led us to obtain new colors which were not observed when these polymers studied separately. For example; coupling PEDOT and PProDOP films in their neutral state resulted in a new red/brown color (L*=59 a*=25 b*=50) which is different from the original colors these polymers show in their neutral states, deep blue (L*=64 a*=-5 b*=-38) and orange (L*=76 a*=31 b*=75), respectively. A full palette of colors is accessible by coupling existing electrochromic polymers by this new bipotentiostatic technique.