Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA

Title: Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA
Authors: Poynton, Fergus E.Hall, James P.Keane, Páraic M.Quinn, Susan J.et al.
Permanent link: http://hdl.handle.net/10197/11596
Date: 27-Jan-2016
Online since: 2020-09-29T09:24:24Z
Abstract: The [Ru(phen)2(dppz)]2+ complex (1) is non-emissive in water but is highly luminescent in organic solvents or when bound to DNA, making it a useful probe for DNA binding. To date, a complete mechanistic explanation for this “light-switch” effect is still lacking. With this in mind we have undertaken an ultrafast time resolved infrared (TRIR) study of 1 and directly observe marker bands between 1280–1450 cm−1, which characterise both the emissive “bright” and the non-emissive “dark” excited states of the complex, in CD3CN and D2O respectively. These characteristic spectral features are present in the [Ru(dppz)3]2+ solvent light-switch complex but absent in [Ru(phen)3]2+, which is luminescent in both solvents. DFT calculations show that the vibrational modes responsible for these characteristic bands are predominantly localised on the dppz ligand. Moreover, they reveal that certain vibrational modes of the “dark” excited state couple with vibrational modes of two coordinating water molecules, and through these to the bulk solvent, thus providing a new insight into the mechanism of the light-switch effect. We also demonstrate that the marker bands for the “bright” state are observed for both Λ- and Δ-enantiomers of 1 when bound to DNA and that photo-excitation of the complex induces perturbation of the guanine and cytosine carbonyl bands. This perturbation is shown to be stronger for the Λ-enantiomer, demonstrating the different binding site properties of the two enantiomers and the ability of this technique to determine the identity and nature of the binding site of such intercalators.
Funding Details: Irish Research Council
Science Foundation Ireland
metadata.dc.description.othersponsorship: Royal Irish Academy/Royal Society International Exchange
Type of material: Journal Article
Publisher: Royal Society of Chemistry
Journal: Chemical Science
Volume: 7
Issue: 5
Start page: 3075
End page: 3084
Keywords: Ruthenium (II) Polypyridyl ComplexesEffective core potentialResonance raman-spectroscopyKinetic-energy densityDipyridiophenazine complexes
DOI: 10.1039/c5sc04514b
Language: en
Status of Item: Peer reviewed
Appears in Collections:Chemistry Research Collection

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