Five-stage near-infrared electrochromism in electropolymerized films composed of alternating cyclometalated bisruthenium and bis-triarylamine segments

Oxidative electropolymerization of cyclometalated bisruthenium complexes [(Nptpy)₂Ru₂(tppyr)](PF₆)₂ and [(Nptpy)₂Ru₂(tpb)](PF₆)₂ produced adherent metallopolymeric films on electrode surfaces, where Nptpy is 4'-(p-N,N-diphenylamino)phenyl-2,2':6',2'-terpyridine, tppyr is the 2,7-bisdeprotonated form of 1,3,6,8-tetra(pyrid-2-yl)pyrene, and tpb is the 3,6-bisdeprotonated form of 1,2,4,5-tetra(pyrid-2-yl)benzene. The resulting polymers are composed of two types of alternating constituent units: tppyr- or tpb-bridged cyclometalated bisruthenium units and biphenyl-bridged bis-triarylamine segments. These films exhibited four well-defined anodic redox couples as a result of the stepwise oxidations of these two units. By manipulating the intervalence charge-transfer transitions of mixed-valent bisruthenium and bis-triarylamine units, five-stage near-infrared electrochromism with stepwise color changes accompanied by good contrast ratio and coloration efficiency has been realized in these films. The film characterization by scanning electronic microscopy and X-ray photoelectron spectroscopy techniques are presented as well.