Correlating on-substrate prepared electrochromes with their solution processed counterparts – towards validating polyazomethines as electrochromes in functioning devices

Abstract

A series of polyazomethines prepared from complementary triphenylamine diamines and thiophene dialdehydes by both solution step-growth and on-substrate polymerizations were examined. The absorbance, electrochemical, and spectroelectrochemical properties of the solution processable polyazomethines were compared to their on-substrate prepared counterparts that were immobilized on ITO coated glass substrates. The on-substrate prepared polymers were found to have enhanced optical and spectroelectrochemical properties compared to their solution processed counterparts. The optoelectronic properties were also contingent on the substitution of the triphenylamine repeating unit with electron donating and withdrawing groups. The on-substrate prepared polyazomethines offered many advantages compared to their counterparts prepared by conventional solution step-growth polymerization, including shorter polymerization times, simpler reaction conditions, straightforward purification, extended duty cycle in simulated electrochromic devices, and enhanced colors, among many others. More importantly, the on-substrate prepared polyazomethines were consistently immobilized on the device electrodes without delamination with extended oxidation/neutralization switching cycles between the neutral and oxidized states.