To elucidate the temporal evolution of the excited states in cisfac- [3] 3+ we recorded fs-transient absorption (TA) spectra after pulsed LMCT excitation at 515 nm in MeCN (Figure , Figure ). The TA spectra bear some similarity with those obtained for [Cr(ddpd)2] 3+ . Global analysis of the data reveals three time constants for cisfac- [3] 3+ (1 = 2.5 ps, 2 = 6.2 ps, 3 = 1.4 ns, Figure , Figure , Figure ). The initial spectrum shows an intense excited state absorption at 740 nm that decays to a new species within 2.5 ps with absorption maxima at 525 and 660 nm. The pseudo-isosbestic point in the area-normalized TA spectra suggests that this transition proceeds from one state to the other, or via intermediate states that do not accumulate (Figure ). Hence, we assign this process to the transition from the initially excited LMCT state to the spin-flip states ( 2 T2/ 2 T1/ 2 E) with an upper limit for the time constant for intersystem crossing (ISC) ISC of 2.5 ps. This is in line with a recent study on a chromium(III) complex where it was not possible to isolate the ISC process with TA spectroscopy alone. Next, the bands sharpen and shift to higher energy with a time constant of 6.2 ps which is consistent with internal conversion (IC) and vibrational cooling (VC) within the doublet excited states 2 T1/ 2 E (Figure ). After 17 ps, the shape of the TA spectra does not change significantly anymore (Figure ) and the 2 T1/ The decay of the 2 E/ 2 T1 states in cisfac- [3] 3+ ( = 1.4 ns) is six orders of magnitude faster than in mer-[Cr(ddpd)2] 3+ ( = 1.12 ms) for which we propose four main reasons: 1) The energy of the 2 T1/ 2 E states in cisfac- [3] 3+ is ca. 0.7 eV smaller than that of the chromium(III) complex which facilitates non-radiative relaxation according to the energy gap law. 2) Multi-phonon relaxation via vibrational overtones of the ligand is favored for cisfac- [3] 3+ as its emission overlaps with the v 2 (C-H) band of the pyridyl ligand (Figure ), while the much weaker v 4 and v 5 overtones are relevant for mer-[Cr(ddpd)2] 3+ . 3) The high spin-orbit coupling in cisfac- [3] 3+ induced by the 4d ion Mo III74 accelerates formally spin-forbidden processes such as the 2 T1/ 2 E 4 A2 relaxation. 106-109 4) The cis-facial coordination of ddpd in cisfac- [3] 3+ enables trigonal distortions in the excited doublet states which can lead to non-radiative deactivation via low-energy mixed states, and which are not available in the more rigid mer-[Cr(ddpd)2] 3+ . It is worth noting that the 4 T2 states that are central to the design of chromium(III) complexes are irrelevant for the photophysics in molybdenum(III) complexes because of their intrinsically much higher energy (Figure ).