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
详细信息 查看全文
- 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 
(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 (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 
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 solvent relaxation predominantly involves collective translationalmotions of ions. It drives the 3IL 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.
(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 (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 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 solvent relaxation predominantly involves collective translationalmotions of ions. It drives the 3IL 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.