Highly electron-accepting viologen derivatives, o-carborane viologens (CbV²⁺), and their iron based-supramolecular polymers (FeSPs) with tunable optoelectronic properties have been reported. Carborane viologens show excellent electron redox properties with low reduction threshold (−0.55 V) and three redox states (divalent cation, radical cation and neutral), which were used to fabricate high-performance electrochromic devices (ECDs). The enhanced photocatalytic hydrogen evolution of the CbV²⁺-based FeSP was achieved (105 times more than CbMV²⁺, 2 times more than viologen-based FeSP) due to its multi-redox center, narrow band gaps, wide visible light absorption (∼580 nm), and especially the metal–ligand charge transfer (MLCT) process. This contribution provides important information for designing and understanding novel viologens and will greatly expand the scope of photocatalysis.