Photophysical Properties of Ruthenium(II) Polypyridyl DNA Intercalators: Effects of the Molecular Surroundings Investigated by Theory

Abstract

The environmental effects on the structural and photophysical properties of [Ru(L)2 (dppz)](2+) complexes (L=bpy=2,2'-bipyridine, phen=1,10-phenanthroline, tap=1,4,5,8-tetraazaphenanthrene; dppz=dipyrido[3,3-a:2',3'-c]phenazine), used as DNA intercalators, have been studied by means of DFT, time-dependent DFT, and quantum mechanics/molecular mechanics calculations. The electronic characteristics of the low-lying triplet excited states in water, acetonitrile, and DNA have been investigated to decipher the influence of the environment on the luminescent behavior of this class of molecules. The lowest triplet intra-ligand (IL) excited state calculated at λ≈800 nm for the three complexes and localized on the dppz ligand is not very sensitive to the environment and is available for electron transfer from a guanine nucleobase. Whereas the lowest triplet metal-to-ligand charge-transfer ((3)MLCT) states remain localized on the ancillary ligand (tap) in [Ru(tap)2 (dppz)](2+), regardless of the environment, their character is drastically modified in the other complexes [Ru(phen)2 (dppz)](2+) and [Ru(bpy)2 (dppz)](2+) upon going from acetonitrile (MLCTdppz/phen or MLCTdppz/bpy) to water (MLCTdppz) and DNA (MLCTphen and MLCTbpy). The change in the character of the low-lying (3) MLCT states accompanying nuclear relaxation in the excited state controls the emissive properties of the complexes in water, acetonitrile, and DNA. The light-switching effect has been rationalized on the basis of environment-induced control of the electronic density distributed in the lowest triplet excited states.

Charge‐Transfer versus Charge‐Separated Triplet Excited States of [ReI(dmp)(CO)3(His124)(Trp122)]+ in Water and in Modified Pseudomonas aeruginosa Azurin Protein

“…The excited‐state properties of isolated metal complexes are the subject of numerous computational investigations based on electronic structure theory and quantum dynamics for the interpretation of their fascinating behavior . However, only a few pioneering studies have been devoted to the effects of the molecular surroundings on these properties . As a paradigmatic example, one can cite the study of the emission properties and absorption spectra of organometallic Ru II DNA intercalators or of a Re I complex probe for DNA‐mediated charge transport …”

“…However, only a few pioneering studies have been devoted to the effects of the molecular surroundings on these properties . As a paradigmatic example, one can cite the study of the emission properties and absorption spectra of organometallic Ru II DNA intercalators or of a Re I complex probe for DNA‐mediated charge transport …”

Tuning the Luminescent Properties of Ruthenium(II) Amino‐1,10‐Phenanthroline Complexes by Varying the Position of the Amino Group on the Heterocycle

“…The electronic absorption spectra of all compounds under investigation are typical for Ru‐bpy complexes ,. It is well known that the intensive bands at 250–300 nm in their spectra correspond to π‐π* ligand−ligand charge transfer transitions.…”

Modeling DNA electronic circular dichroism by QM/MM methods and Frenkel Hamiltonian

“…Furthermore, it is important to precisely unravel the distortions induced in the DNA structure by the presence of lesions [12]. At the same time, it is still important to achieve a good comprehension of the aggregates formed by the interaction between DNA and relatively small endogenous or exogenous compounds that may subsequently induce lesions for instance through photosensitization [13][14][15][16][17][18][19][20]. At the same time, it is still important to achieve a good comprehension of the aggregates formed by the interaction between DNA and relatively small endogenous or exogenous compounds that may subsequently induce lesions for instance through photosensitization [13][14][15][16][17][18][19][20].…”

“…Indeed, DNA chromophores being embedded in a complex inhomogeneous environment, a multiscale treatment based on hybrid quantum mechanics/molecular mechanics (QM/MM) is compulsory to correctly reproduce the excited state energies and the spectroscopic properties, as shown by some of us for similar systems [13][14][15][16][17]38]. Indeed, DNA chromophores being embedded in a complex inhomogeneous environment, a multiscale treatment based on hybrid quantum mechanics/molecular mechanics (QM/MM) is compulsory to correctly reproduce the excited state energies and the spectroscopic properties, as shown by some of us for similar systems [13][14][15][16][17]38].…”