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  4. Dual Luminescence, Interligand Decay, and Nonradiative Electronic Relaxation of Cyclometalated Iridium Complexes in Solution
 
research article

Dual Luminescence, Interligand Decay, and Nonradiative Electronic Relaxation of Cyclometalated Iridium Complexes in Solution

Pomarico, E.  
•
Silatani, M.  
•
Messina, F.  
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2016
Journal Of Physical Chemistry C

Femtosecond broadband photoluminescence studies are presented for Ir(ppy)(3) (Ir1), Ir(ppy)(2)(pic) (Ir2), Ir(ppy)(2)(bpy)(PF6) (Ir3), Ir(ppz)(3) (Ir4), and Ir(ppz)(2)dipy (Ir5) (where ppy = 2-phenylpyridine, pic = picolinate, bpy = 2,2'-bipyridine, ppz = 1-phenylpyrazole, and dipy = 5-phenyldipyrrinato) in solution. Upon 400-nm excitation of Ir1-Ir3, we observed a prompt population of the lowest MLCT states. The higher states decay on an ultrafast time scale (<100 fs), whereas the lowest (MLCT)-M-3 state undergoes further vibrational relaxation on a 1-ps time scale. In Ir3, this relaxation is accompanied by an interligand decay from the ppy to the bpy ligand in similar to 1.5 ps. For the ppy-containing complexes (Ir1 and Ir2), we found that, at 100 ps, the luminescence is red-shifted with respect to the steady-state emission. This is explained in terms of a time-delayed dual luminescence, which we attribute to a double-well minimum configuration of the lowest emitting triplet states involving the ppy moiety. Ir4 shows a prompt population of the lowest excited state, which then undergoes vibrational relaxation in similar to 0.5 ps. Finally, at short times, Ir5 exhibits fluorescence from the lowest (LC)-L-1 state, which decays in similar to 100 fs to the manifold of (LC)-L-3 states. Overall, this study shows that, although the ultrafast relaxation to the lowest electronic states is quite similar to that of other transition-metal complexes, most of the differences occur at the lowest emissive states, with effects such as time-delayed dual fluorescence, interligand decay, and nonradiative relaxation to the ground or lower-lying metal-centered states. Understanding these effects is crucial for obtaining optimal performances of iridium complexes, calling for further iterations between chemical synthesis and photophysical studies to optimize these complexes.

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Type
research article
DOI
10.1021/acs.jpcc.6b04896
Web of Science ID

WOS:000381236100021

Author(s)
Pomarico, E.  
Silatani, M.  
Messina, F.  
Braem, O.  
Cannizzo, A.  
Barranoff, E.
Klein, J. H.
Lambert, C.
Chergui, M.  
Date Issued

2016

Publisher

American Chemical Society

Published in
Journal Of Physical Chemistry C
Volume

120

Issue

30

Start page

16459

End page

16469

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LSU  
Available on Infoscience
October 18, 2016
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/130370
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