Ligand-centred fluorescence and electronic relaxation cascade at vibrational time scales in transition-metal complexes.
J Phys Chem Lett
; 6(22): 4475-80, 2015 Nov 19.
Article
in En
| MEDLINE
| ID: mdl-26509329
ABSTRACT
Using 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 ((3)MLCT) 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 â¼1.6 eV from the (1)LC state to the lowest (3)MLCT 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.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Language:
En
Journal:
J Phys Chem Lett
Year:
2015
Document type:
Article
Affiliation country:
Switzerland