Excited-state dynamics of [Re(Etpy)(CO)
3(bpy)]
+ was studied in three imidazo
lium ionic
liquids by time-reso
lved IR and emission spectroscopy on the picosecond to nanosecond time sca
le. Low-
lying excited stateswere characterized by TD-DFT ca
lcu
lations, which a
lso provided mo
lecu
lar dipo
le moment vectors in there
levant e
lectronic states. TRIR spectra in ionic
liquids show initia
l popu
lations of two excited states:predominant
ly bpy-
loca
lized
3IL and
3MLCT, characterized by
(CO) bands shifted to
lower and higherfrequencies, respective
ly, re
lative to the ground state. Interna
l conversion of
3IL to the
lowest trip
let
3MLCToccurred on a time sca
le commensurate with so
lvent re
laxation. The
(CO) IR bands of the
3MLCT stateundergo a dynamic shift to higher wavenumbers during re
laxation. Its three-exponentia
l kinetics weredetermined and attributed to vibrationa
l coo
ling (units of picoseconds), energy dissipation to the bu
lk so
lvent(tens of picoseconds), and so
lvent re
laxation, the
lifetime of which increases with increasing viscosity: [EMIM]BF
4 (330 ps) &
lt; [BMIM]BF
4 (470 ps) &
lt; [BMIM]PF
6 (1570 ps). Time-reso
lved phosphorescence spectra in[BMIM]PF
6 show a ~2 ns drop in intensity due to the
3IL
3MLCT conversion and a dynamic Stokes shiftto
lower energies with a
lifetime decreasing from 1.8 ns at 21
C to 1.1 ns at 37
C, due to decreasingviscosity of the ionic
liquid. It is proposed that so
lvent re
laxation predominant
ly invo
lves co
llective trans
lationa
lmotions of ions. It drives the
3IL
3MLCT conversion, increases charge reorganization in the
lowest excited-state
3MLCT, and affects vibrationa
l anharmonic coup
ling, which together cause the dynamic shift of excited-state IR bands. TRIR spectroscopy of carbony
l-diimine comp
lexes emerges as a new way to investigatevarious aspects of so
lvation dynamics, whi
le the use of s
low
ly re
laxing ionic
liquids offers new insight intothe photophysics of Re(I) carbony
l po
lypyridy
ls.