  An explanation is provided for the ultrafast photo-excited electron dynamics
in low-spin Ruthenium (II) organic complexes. The experimentally-observed
singlet to triplet decay in the metal-to-ligand charge-transfer (MLCT) states
contradicts the expectation that the system should oscillate between the
singlet and triplet states in the presence of a large spin-orbit coupling and
the absence of a significance change in metal-ligand bond length. This dilemma
is solved with a novel quantum decay mechanism that causes a singlet to triplet
decay in about 300 femtoseconds. The decay is mediated by the triplet
metal-centered state ($^3$MC) state even though there is no direct coupling
between the $^1$MLCT and $^3$MC states. The coupling between the $^3$MLCT and
$^3$MC via excited phonon states leads to vibrational cooling that allows the
local system to dissipate the excess energy. In the relaxed state, the
population of the $^3$MC state is low and the metal-ligand bond length is
almost unchanged with respect to the initial photoexcited state, in agreement
with experiment.
