A series of unsaturated ferrocene derivatives with the formula Fc-CH = CH-X (X ≡ CHO, CN, COCH 3 , COOCH 3 , 4-py; Fc, ferrocene) were synthesized. They were found to exhibit reversible one-electron oxidation and two one-electron reduction steps. Quenching of the excited state of Ru(bpy) 3 2 + (bpy, 2,2 -bipyridine) by the ferrocene derivatives was also studied. Quenching occurs mainly via electron transfer on the ferrocenyl group in acetonitrile. The results are confirmed by molecular orbital calculations using the CNDO method. A quenching mechanism is suggested. The bimolecular quenching rate constants were obtained from the Stern-Volmer equation. Linear relationships are obtained for a plot of log K q vs. - δG of electron transfer.