Electrochromic and photoelectrochromic switching devices based on aryl amine redox chemistry

Abstract

Electrochromic Materials are of interest as fundamental components in smart windows, displays, and fabrics. A new class of organic arylamine molecular electrochromes (both ionic and neutral) has been developed to afford optimal optical and electrochemical switching properties in the absorptive/transmissive electrochromic device state. By controlling the number of redox active units, structuring their internal electronic coupling and alternating the charge state of the electrochrome, a range of optical states are afforded. N, N, N´, N´-Tetraanisyl-1,4- phenylenediame (TAPD) is optimized for use as multi-colored electrochromic molecular dye in the type I (solution) device state. Anionic polyarylamines are prepared and tested in transmissive singular type I electrochromic devices. The application of a small bias (2 V) leads to highly colored stable radical zwitterions. Lack of formal net charge in the oxidized form of the molecule influences its mass transport in the device to yield faster switching times. Devices with these anionic electrochromes also exhibit faster open circuit bleaching kinetics in contrast to neutral devices. In addition to their device studies, stable radical zwitterions have been synthesized (via chemical oxidation), and characterized using cyclic voltammetry, electron paramagnetic resonance (EPR) spectroscopy and optical spectroscopy. Information gained from these studies has led to an improved understanding of the rational design of isolable radical zwitterions. The phenomenon of electrochromism is further demonstrated in a novel redox auxiliary (RA) photoelectrochromic switch. An amino substituted norbornadiene (AA-N-Ts) undergoes photochemical rearrangement to its colorless quadricyclane isomer (AA-Q-Ts), which can be reversibly transformed back to the yellow AA-N-Ts upon oxidative catalysis at an electrode in solution. Similarly, amino substituted azobenzene derivatives isomerize between the contracted (cis) form and the expanded (trans) form as a result of photochemical and electrochemical stimuli, respectively. Using the technology of type I electrochromic devices, the photoelectrochromic switching of these systems is demonstrated with large duty cycles (~1000 cycles). The photoelectrochromic device (PECD) also provides an analytical platform for the study of redox auxiliary catalysis. A new photoelectrochromic switching media has been developed for cycling aromatic photoelectrochromic systems. The general utility of this media in the photoelectrochromic cycling redox auxiliary systems is also presented.