a series of sulfur-bridged 2,2′-viologens, 2,2′-thienoviologens (2,2′-sv2 ) with propyl bridge and hydroxyl bridges, are synthesized for the first time. the 2,2′-thienoviologens exhibited improved visible-light absorption, narrow energy gap, more negative reduction potential (160 mv lower than 4,4′-thienoviologens) and more stable free radical states compared with 4,4′-thienoviologens and parent 2,2′-viologens.
