Return electron transfer (RET) and intersystem crossing (ISC) of [(tpy)Ru-III(tpy-ph-tpy)(2),Co-4(II)(tpy)](5+) (tpy = 2,2':6',2"-terpyridine and tpy-ph-tpy = 1,4-bis [2,2':6',2"-terpyridine-4'-yl] benzene) and [(tpy)Ru-II(tpy-tpy)-Co (III)(tpy)](5+) (tpy-tpy = 6',6"-bis(2-pyridyl)-2,2':4',4":2",2"'-quarter-pyridyne) produced on the subpicosecond laser excitation have been investigated in a wide temperature range. A biexponential recovery process of [(tpy)Ru-II(tpy-ph-tpy)Co-III(tpy)](5+) and [Co-III(t)] = [Co-2(III)(0)](1 - [f(alpha) exp(-k(alpha)t) + f(beta) exp(-k(beta)t)]) occurs immediately after the production of [Ru-2(III)(tpy)(tpy-pph-tpy)Co-2(II)(tpy)](5+) in the excited-state electron-transfer quenching of [(tpy)Ru-II(tpy-ph-tpy)Co-III(tpy)](5+). Four parameters of biexponential recovery, k(alpha), f(alpha), k(beta) and fbeta in a range of 180-300 K, are interpreted in terms of RET and ISC reactions among three states: [(tpy)Ru-2(III) (tpy-ph-tpy)Co-2(II)(tpy)](5+), [(tpy)Ru-2(III)(tpy-tpy)Co-4(II)(tpy)](5+), and [(tpy)Ru-II(tpy-ph-tpy)Co-III(tpy)](5+). RET of [(tpy)Ru-2(III)(tpy-ph-tpy)Co-2(II)(tpy)](5+) regenerating [(tpy)Ru-II(tpy-ph-tpy)Co-III(tpy)](5+) with k(RET(D)) of similar to4 x 10(10) s(-1) competes with doublet-quartet ISC with k(QD) of 0.20 x 10(10) s(-1) at DeltaGdegrees(QD) of 0.044 eV and 2.8 x 10(10) s(-1) at DeltaGdegrees(QD) of -0.01 eV. Meanwhile, the rate constant of the quartet-doublet ISC, k(DQ) (similar to1.6 x 10(10) s(-1) at DeltaGdegrees(QD) of -0.01 eV), is much larger than RET of f(tpy)Ru-2(III)(tpy-ph-tpy)Co-4(II)(tpy)](5+). Dependences of k(QD) on DeltaGdegrees(DQ) give rise to a rough estimation of reorganizational free energy (0.03 eV). As for [(tpy)Ru(II)tpy-tpy)Co-III(tpy)](5+), k(RET(D)), k(DQ), and k(QD) are evaluated to be 2.3 x 10(11) s(-1), 1.5 x 10(11) s(-1) and 1.5 x 10(11) s(-1) at DeltaGdegrees(QD) of -0.01 eV.