Search for "4,4'-bipyridinium salts" in Full Text gives 2 result(s) in Beilstein Journal of Organic Chemistry.
Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123
Beilstein J. Org. Chem. 2019, 15, 1795–1804, doi:10.3762/bjoc.15.173