Electrochromic materials are materials that change color upon an application of a voltage or current. In the Reynolds group, the materials are specifically conjugated polymers that switch from a colored film when in their charge-neutral state, to a colorless film when oxidized. What sets these materials apart from other families of electrochromic materials are the broad range of vibrant colors, as well as switching times on the order of seconds or less, and contrasts over 60% for most of our colors, all within an approximately 1 V window. Potential applications range from color-changing lenses and windows, to signage and displays, from aesthetic designs to smart heat management.
Upper left: demonstration of an electrochromic device switching from a colored to a colorless state upon application of a potential
Lower left: a segmented reflective device1 and an airbrush sprayed butterfly2
Right: an electrochromic window integrated with solar panels
In our group, a family of colored to colorless electrochromic polymers based on dioxythiophenes have been synthesized that span the visible color palette. This has been made possible through developing an understanding of the relationship between the chemical structure and the color of the polymer.3,4,5 The synthetic strategies employed include judicious distribution of electron poor and rich units along the polymer backbone, selectively employing electron donating or withdrawing substituent, or tuning conjugation through steric side chains. These materials are soluble in a range of non-chlorinated solvents, and even in water,6 allowing them to be solution-processed using various roll-to-roll processable techniques.
Left: polymer solutions of the different materials at varying concentrations7
Right: switching contrast of blue electrochromic polymer at different switching speeds8
In addition to processability, solubility allows electrochromic solutions to be blended together, to fine-tune coloration as well as to access colors such as blacks and browns. Specific colors can even be targeted through predictable color-mixing of the solutions. Through combining solutions from our large library of electrochromic polymers, a fast-switching colored to colorless film of virtually any color can be produced.
Left: cyan, magenta and yellow electrochromic solutions are blended together to give vibrant new colors9
Right: orange and periwinkle solutions are mixed to give a reddish-brown hue. Prototype lenses are fabricated to demonstrate the switching of the brown in an actual device10
1Argun, A.A., Berard, M., Aubert, P.-H., Reynolds, J.R. Adv. Mater. 2005, 17, 422-426.
2Vasilyeva, S.V., Beaujuge, P.M., Wang, S., Babiarz, J.E., Ballarotto, V.W., Reynolds, J.R. ACS Appl. Mater. Interf. 2011, 3, 1022-1032.
3Amb, C.M., Dyer, A.L., Reynolds, J.R. Chem. Mater. 2011, 23, 397-415.
4Kerszulis, J.A., Amb, C.M., Dyer, A.L., Reynolds, J.R. Macromolecules, 2014, 47, 5462-5469.
5Kerszulis, J.A., Johnson, K.E., Kuepfert, M., Khoshabo, D., Dyer, A.L., Reynolds, J.R. J. Mater. Chem. C, 2015, 3, 3211-3218.
6Shi, P., Amb, C.M., Dyer, A.L., Reynolds, J.R. ACS Appl. Mater. Interf. 2012, 4, 6512-6521.
7Dyer, A.L., Thompson, E.J., Reynolds, J.R. ACS Appl. Mater. Interf. 2011, 3, 1787-1795.
8Beaujuge, P.M., Amb, C.M., Reynolds, J.R. Adv. Mater. 2010, 22, 5383-5387.
9Bulloch, R.H., Kerszulis, J.A., Dyer, A.L., Reynolds, J.R. ACS Appl. Mater. Intef. 2015, 7, 1406-1412.
10Osterholm, A.M., Shen, D.E., Kerszulis, J.A., Bulloch, R.H., Keupfert, M., Dyer, A.L., Reynolds, J.R. ACS Appl. Mater. Interf. 2015, 7, 1413-1421.