1,1'-Propylene-2,2'-bipyridilium 1,1'-Propylene-2,2'-bipyridyl 121013-72-7 Dipyrido(1,2-a:2',1'-c)pyrazine, 6,7-dihydro-6-methyl-, radical ion (1+) Pdq dibromide Pdq(+) Pdq-radical Propylene diquat