Messina, FabrizioPomarico, EnricoSilatani, MahsaBaranoff, EtienneChergui, Majed2016-02-162016-02-162016-02-16201510.1021/acs.jpclett.5b02146https://infoscience.epfl.ch/handle/20.500.14299/124064WOS:000365460700005Using femtosecond-resolved photoluminescence up-conversion, we report the observation of the fluorescence of the high-lying ligand-centered (LC) electronic state upon 266 nm excitation of an iridium complex, Ir(ppy)(3), with a lifetime of 70 +/- 10 fs. It is accompanied by a simultaneous emission of all lower-lying electronic states, except the lowest triplet metal-to-ligand charge-transfer ((MLCT)-M-3) state that shows a rise on the same time scale. Thus, we observe the departure, the intermediate steps, and the arrival of the relaxation cascade spanning similar to 1.6 eV from the (LC)-L-1 state to the lowest 3MLCT state, which then yields the long-lived luminescence of the molecule. This represents the first measurement of the total relaxation time over an entire cascade of electronic states in a polyatomic molecule. We find that the relaxation cascade proceeds in <= 10 fs, which is faster than some of the highest-frequency modes of the system. We invoke the participation of the latter modes in conical intersections and their overdamping to low-frequency intramolecular modes. On the basis of literature, we also conclude that this behavior is not specific to transition-metal complexes but also applies to organic molecules.text::journal::journal article::research article