Solvation-Driven Excited-State Dynamics of [Re(4-Et-Pyridine)(CO)3(2,2'-bipyridine)]+ in Imidazolium Ionic Liquids. A Time-Resolved Infrared and Phosphorescence Study
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- 作者：Ana Maria Blanco-Rodrí ; guez ; Kate L. Ronayne ; Stanislav Zá ; li ; Jan Skora ; Martin Hof ; Antoní ; n Vlek ; Jr.
- 刊名：Journal of Physical Chemistry A
- 出版年：2008
- 出版时间：April 24, 2008
- 年：2008
- 卷：112
- 期：16
- 页码：3506 - 3514
- 全文大小：284K
- 年卷期：v.112,no.16(April 24, 2008)
- ISSN：1520-5215
文摘
Excited-state dynamics of [Re(Etpy)(CO)3(bpy)]+ was studied in three imidazolium ionic liquids by time-resolved IR and emission spectroscopy on the picosecond to nanosecond time scale. Low-lying excited stateswere characterized by TD-DFT calculations, which also provided molecular dipole moment vectors in therelevant electronic states. TRIR spectra in ionic liquids show initial populations of two excited states:predominantly bpy-localized 3IL and 3MLCT, characterized by 
nu.gif" BORDER=0 >(CO) bands shifted to lower and higherfrequencies, respectively, relative to the ground state. Internal conversion of 3IL to the lowest triplet 3MLCToccurred on a time scale commensurate with solvent relaxation. The nu.gif" BORDER=0 >(CO) IR bands of the 3MLCT stateundergo a dynamic shift to higher wavenumbers during relaxation. Its three-exponential kinetics weredetermined and attributed to vibrational cooling (units of picoseconds), energy dissipation to the bulk solvent(tens of picoseconds), and solvent relaxation, the lifetime of which increases with increasing viscosity: [EMIM]BF4 (330 ps) < [BMIM]BF4 (470 ps) < [BMIM]PF6 (1570 ps). Time-resolved phosphorescence spectra in[BMIM]PF6 show a ~2 ns drop in intensity due to the 3IL 
ntities/rarr.gif"> 3MLCT conversion and a dynamic Stokes shiftto lower energies with a lifetime decreasing from 1.8 ns at 21 ntities/deg.gif">C to 1.1 ns at 37 ntities/deg.gif">C, due to decreasingviscosity of the ionic liquid. It is proposed that solvent relaxation predominantly involves collective translationalmotions of ions. It drives the 3IL ntities/rarr.gif"> 3MLCT conversion, increases charge reorganization in the lowest excited-state 3MLCT, and affects vibrational anharmonic coupling, which together cause the dynamic shift of excited-state IR bands. TRIR spectroscopy of carbonyl-diimine complexes emerges as a new way to investigatevarious aspects of solvation dynamics, while the use of slowly relaxing ionic liquids offers new insight intothe photophysics of Re(I) carbonyl polypyridyls.
nu.gif" BORDER=0 >(CO) bands shifted to lower and higherfrequencies, respectively, relative to the ground state. Internal conversion of 3IL to the lowest triplet 3MLCToccurred on a time scale commensurate with solvent relaxation. The nu.gif" BORDER=0 >(CO) IR bands of the 3MLCT stateundergo a dynamic shift to higher wavenumbers during relaxation. Its three-exponential kinetics weredetermined and attributed to vibrational cooling (units of picoseconds), energy dissipation to the bulk solvent(tens of picoseconds), and solvent relaxation, the lifetime of which increases with increasing viscosity: [EMIM]BF4 (330 ps) < [BMIM]BF4 (470 ps) < [BMIM]PF6 (1570 ps). Time-resolved phosphorescence spectra in[BMIM]PF6 show a ~2 ns drop in intensity due to the 3IL ntities/rarr.gif"> 3MLCT conversion and a dynamic Stokes shiftto lower energies with a lifetime decreasing from 1.8 ns at 21 ntities/deg.gif">C to 1.1 ns at 37 ntities/deg.gif">C, due to decreasingviscosity of the ionic liquid. It is proposed that solvent relaxation predominantly involves collective translationalmotions of ions. It drives the 3IL ntities/rarr.gif"> 3MLCT conversion, increases charge reorganization in the lowest excited-state 3MLCT, and affects vibrational anharmonic coupling, which together cause the dynamic shift of excited-state IR bands. TRIR spectroscopy of carbonyl-diimine complexes emerges as a new way to investigatevarious aspects of solvation dynamics, while the use of slowly relaxing ionic liquids offers new insight intothe photophysics of Re(I) carbonyl polypyridyls.