Vibrational Relaxation and Redistribution Dynamics in Ruthenium(II) Polypyridyl-Based Charge-Transfer Excited States: A Combined Ultrafast Electronic and Infrared Absorption Study
| Autor: | James K. McCusker, Michael Towrie, Allison M. Brown, Ian P. Clark, Catherine E. McCusker, Antonín Vlček, Ana María Blanco-Rodríguez, Monica C Carey |
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| Rok vydání: | 2018 |
| Předmět: |
010405 organic chemistry
Chemistry Infrared spectroscopy Chromophore 010402 general chemistry 01 natural sciences 0104 chemical sciences Bipyridine chemistry.chemical_compound Intramolecular force Picosecond Excited state Vibrational energy relaxation Physical chemistry Density functional theory Physical and Theoretical Chemistry |
| Zdroj: | The Journal of Physical Chemistry A. 122:7941-7953 |
| ISSN: | 1520-5215 1089-5639 |
| Popis: | Ultrafast time-resolved electronic and infrared absorption measurements have been carried out on a series of Ru(II) polypyridyl complexes in an effort to delineate the dynamics of vibrational relaxation in this class of charge transfer chromophores. Time-dependent density functional theory calculations performed on compounds of the form [Ru(CN-Me-bpy) x(bpy)3-x]2+ ( x = 1-3 for compounds 1-3, respectively, where CN-Me-bpy is 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine and bpy is 2,2'-bipyridine) reveal features in their charge-transfer absorption envelopes that allow for selective excitation of the Ru(II)-(CN-Me-bpy) moiety, the lowest-energy MLCT state(s) in each compound of the series. Changes in band shape and amplitude of the time-resolved differential electronic absorption data are ascribed to vibrational cooling in the CN-Me-bpy-localized 3MLCT state with a time constant of 8 ± 3 ps in all three compounds. This conclusion was corroborated by picosecond time-resolved infrared absorption measurements; sharpening of the CN stretch in the 3MLCT excited state was observed with a time constant of 3.0 ± 1.5 ps in all three members of the series. Electronic absorption data acquired at higher temporal resolution revealed spectral modulation over the first 2 ps occurring with a time constant of τ = 170 ± 50 fs, in compound 1; corresponding effects are significantly attenuated in compound 2 and virtually absent in compound 3. We assign this feature to intramolecular vibrational redistribution (IVR) within the 3MLCT state and represents a rare example of this process being identified from time-resolved electronic absorption data for this important class of chromophores. |
| Databáze: | OpenAIRE |
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