Multistate near-infrared electrochromism and electron transfer in different oligotriphenylamine systems

Four oligomeric triarylamine compounds (diamine la, triamine lb, tetramine lc and pentamine 1d) were prepared and characterized by 1H NMR, mass spectrometry and elemental analysis. The combined results of cyclic voltammetry, square-wave voltammetry and UV vis NIR spectroelectrochemistry, as well as density functional theory, reveal that compounds la ld display two to five steps of oxidation processes, respectively, and the AE1/2 and Kc values were still remarkable for the relatively long pentamine, though they all decreased with an increase of the triphenylamine unit. These four compounds all exhibit fascinating redox-tuned multiple NIR absorption characteristics, and a completely reversible multicolor electrochromism for each of them could be synchronously realized. The associated mono cationic [1a]-[1d](+) could be classified as moderately-coupled Robin Day class H mixed-valence systems, which could be stabilized by spin delocalization over at least two adjacent amine units. (C) 2017 Elsevier Ltd. All rights reserved.