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  4. Ultrafast Excited-State Dynamics ef [Re(L)(CO)(3)(bpy)](n) Complexes: Involvement of the Solvent
 
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research article

Ultrafast Excited-State Dynamics ef Re(L)(CO)(3)(bpy) Complexes: Involvement of the Solvent

El Nahhas, Amal  
•
Cannizzo, Andrea  
•
van Mourik, Frank  
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2010
The Journal of Physical Chemistry A

Ultrafast excited-state dynamics of Re(L)(CO)(3)(bpy) (L = Cl, Br, n = 0; L = 4-ethyl-pyridine (Etpy), n = 1+; bpy = 2,2'-bipyridine) have been investigated in dimethylformamide (DMF) solution by fluorescence up-conversion (FIUC) and UV - vis transient absorption (TA) with similar to 100 is time,resolution. TA was also measured in the [1-ethyl-3-methyl-imidazolium]BF4 ionic liquid. The complexes show a very broad fluorescence band at 540-550 nm at zero time delay, which decays with 100-140 Is (depending on L) by intersystem crossing (ISC) to pi pi* intraligand ((IL)-I-3) and a Re(L)(CO)(3) -> bpy charge-transfer ((CT)-C-3) excited states. A second emission decay component (1.1-1.7 ps). apparent in the red part of the spectrum, is attributed to (IL)-I-3 -> (CT)-C-3 conversion, leaving phosphorescence from the lowest (CT)-C-3 state as the only emission signal at longer time delays. The triplet conversion is slower in DMF? than acetonitrile, commensurate with solvation times. Full assignment of the excited-state absorption at long delay times is obtained by TD-DFT calculations on the lowest triplet state, showing,2 that the 373 nm band is the sole diagnostics of bpy reduction in the CT excited state. Bands in the visible are clue to Ligand-to-Metal-Charge-Transfer (LMCT) transitions. Time-resolved UV - vis absorption spectra exhibit a units-of-ps rise of all absorption features attributed to (IL)-I-3 -> (CT)-C-3 conversion as well as electronic and vibrational relaxation, and a similar to 15 ps rise of only the 373 nm pi pi*(bpy(center dot-)) band which slows down to similar to 1 ns in the ionic liquid solvent. It is proposed that this slow relaxation originates mainly from restructuring of solvent molecules that are found very close to the metal center, inserted between the ligands. The solvent thus plays a key role in controlling the intramolecular charge separation, and this effect may well be operative other classes of metal-based molecular complexes.

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Type
research article
DOI
10.1021/jp101999m
Web of Science ID

WOS:000278300600003

Author(s)
El Nahhas, Amal  
•
Cannizzo, Andrea  
•
van Mourik, Frank  
•
Blanco-Rodriguez, Ana Maria
•
Zalis, Stanislav
•
Vlcek, Antonin
•
Chergui, Majed  
Date Issued

2010

Publisher

American Chemical Society

Published in
The Journal of Physical Chemistry A
Volume

114

Start page

6361

End page

6369

Subjects

Resolved Infrared-Spectroscopy

•

Carbonyl-Diimine Complexes

•

Atoms Ga-Kr

•

Femtosecond Fluorescence

•

Resonance Raman

•

Ionic Liquids

•

Photophysical Properties

•

Homogeneous Catalysts

•

Ir Absorption

•

Stokes Shift

Peer reviewed

NON-REVIEWED

Written at

EPFL

EPFL units
LSU  
Available on Infoscience
October 4, 2010
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/54799
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