Excited-state dy
namics of [Re(Etpy)(CO)
3(bpy)]
+ was studied i
n three imidazolium io
nic liquids by time-resolved IR a
nd emissio
n spectroscopy o
n the picoseco
nd to
na
noseco
nd time scale. Low-lyi
ng excited stateswere characterized by TD-DFT calculatio
ns, which also provided molecular dipole mome
nt vectors i
n thereleva
nt electro
nic states. TRIR spectra i
n io
nic liquids show i
nitial populatio
ns of two excited states:predomi
na
ntly bpy-localized
3IL a
nd
3MLCT, characterized by
nu.gif" BORDER=0 >(CO) ba
nds shifted to lower a
nd higherfreque
ncies, respectively, relative to the grou
nd state. I
nter
nal co
nversio
n of
3IL to the lowest triplet
3MLCToccurred o
n a time scale comme
nsurate with solve
nt relaxatio
n. The
nu.gif" BORDER=0 >(CO) IR ba
nds of the
3MLCT stateu
ndergo a dy
namic shift to higher wave
numbers duri
ng relaxatio
n. Its three-expo
ne
ntial ki
netics weredetermi
ned a
nd attributed to vibratio
nal cooli
ng (u
nits of picoseco
nds), e
nergy dissipatio
n to the bulk solve
nt(te
ns of picoseco
nds), a
nd solve
nt relaxatio
n, the lifetime of which i
ncreases with i
ncreasi
ng viscosity: [EMIM]BF
4 (330 ps) < [BMIM]BF
4 (470 ps) < [BMIM]PF
6 (1570 ps). Time-resolved phosphoresce
nce spectra i
n[BMIM]PF
6 show a ~2
ns drop i
n i
nte
nsity due to the
3IL
ntities/rarr.gif">
3MLCT co
nversio
n a
nd a dy
namic Stokes shiftto lower e
nergies with a lifetime decreasi
ng from 1.8
ns at 21
ntities/deg.gif">C to 1.1
ns at 37
ntities/deg.gif">C, due to decreasi
ngviscosity of the io
nic liquid. It is proposed that solve
nt relaxatio
n predomi
na
ntly i
nvolves collective tra
nslatio
nalmotio
ns of io
ns. It drives the
3IL
ntities/rarr.gif">
3MLCT co
nversio
n, i
ncreases charge reorga
nizatio
n i
n the lowest excited-state
3MLCT, a
nd affects vibratio
nal a
nharmo
nic coupli
ng, which together cause the dy
namic shift of excited-state IR ba
nds. TRIR spectroscopy of carbo
nyl-diimi
ne complexes emerges as a
new way to i
nvestigatevarious aspects of solvatio
n dy
namics, while the use of slowly relaxi
ng io
nic liquids offers
new i
nsight i
ntothe photophysics of Re(I) carbo
nyl polypyridyls.