Electrochemical and spectroelectrochemical characterization of hexacoordinate polypyridine silicon complexes show that they are fitting candidates for electrochromic applications. Tris(bipyridine)silicon(IV), [Si(bpy)3]+4, is colorless in acetonitrile as the hexafluorophosphate salt, with two overlapping peaks at 327 and 341 nm. Successive reduction by up to three electrons turns the solution green, as the intensity of the 327/341 nm peaks decrease and two new peaks emerge, one around 390 nm and a very broad transition centered around 800 nm. Each reduction is fully reversible and entirely based on the bipyridine ligands, and full conversion to each charged state is realized at the proper potential. Tris(4,4’–di–tert–butyl–2,2’–bipyridine)silicon(IV), [Si(4dtbbpy)3]+4, and tris(5,5’–dimethyl–2,2’–bipyridine)silicon(IV), [Si(5dmbpy)3]+4, are similar with initial overlapping peaks at 321/334 nm and 340/356 nm, respectively for the two complexes. These peaks disappear on reduction and a sharp peak at 391 nm and a broad peak at 807 nm both emerge for [Si(4dtbbpy)3]n, whereas these peaks are at 413 and 830 nm for [Si(5dmbpy)3]n. The complexes are both colorless in solution as the +4 species then green upon reduction. Bis(4’–tolylterpyridine)silicon(IV), [Si(ttpy)2]+4, is slightly yellow in acetonitrile as the hexafluorophosphate salt, with a sharp peak at 302 nm and two overlapping peaks at 378 and 407 nm. Reduction by two electrons turns the solution blue with emergence of a broad peak centered around 653 nm, and reduction by a further two electrons turn the solution reddish–purple with a peak at 514 nm that tails out into the infrared.
