Vibrational Relaxation and Redistribution Dynamics in Ruthenium(II) Polypyridyl-Based Charge-Transfer Excited States: A Combined Ultrafast Electronic and Infrared Absorption Study

0494623 - ÚFCH JH 2019 RIV US eng J - Journal Article
Brown, A. M. - McCusker, C. E. - Carey, M. C. - Blanco-Rodríguez, A. M. - Towrie, M. - Clark, I. P. - Vlček, Antonín - McCusker, J. K.
Vibrational Relaxation and Redistribution Dynamics in Ruthenium(II) Polypyridyl-Based Charge-Transfer Excited States: A Combined Ultrafast Electronic and Infrared Absorption Study.
Journal of Physical Chemistry A. Roč. 122, č. 40 (2018), s. 7941-7953. ISSN 1089-5639. E-ISSN 1520-5215
R&D Projects: GA ČR GA17-01137S
Institutional support: RVO:61388955
Keywords : Chromophores * Charge transfer * Density functional theory
OECD category: Physical chemistry
Impact factor: 2.641, year: 2018

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-localized3MLCT 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 the3MLCT 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 Γ = 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 the3MLCT state and represents a rare example of this process being identified from time-resolved electronic absorption data for this important class of chromophores.
Permanent Link: http://hdl.handle.net/11104/0287734