Jean-Louis Heully

Spin-orbit effects on the photophysical properties of Ru(bpy)32+

We present in this article a detailed study of the photophysics of the Ru(bpy)(3)(2+) complex based on a formalism using density functional theory and an a posteriori treatment of the spin-orbit coupling. The absorption and emission spectra were computed and a very good agreement was obtained with the available experimental data. This work also reveals for the first time that the triplet metal-centered (MC) dd state cannot deactivate radiatively and corresponds to a transient structure for the nonradiative de-excitation of the triplet metal-to-ligand charge transfer (MLCT) state. Thus, a competition takes place between the luminescence of the MLCT state and nonradiative decay back to the ground state via population of the MC state. This radiationless return to the ground state occurs via a deactivation funnel which has been characterized for the first time by optimizing the minimum energy crossing point between the triplet MC and singlet ground state potential energy surfaces. Its low-lying energy position relative to the energy necessary to access the MC minimum suggests that this funnel will be readily accessible.

Can a functionalized phosphine ligand promote room temperature luminescence of the [Ru(bpy)(tpy)]2+ core?

Unexpected room temperature luminescence is observed and rationalized by highly challenging excited state calculations for a functionalized phosphine ligand coordinated on the [Ru(bpy)(tpy)](2+) core.

Electronic peculiarities of the excited states of [RuN5C]+vs. [RuN6]2+ polypyridine complexes: insight from theory

The ground state, oxidized ground state, (3)MLCT and (3)MC excited states have been studied by DFT and TDDFT for two Ru(II) complexes bearing an N(6) or N(5)C coordination sphere. The effect of replacing one Ru-N dative bond by one Ru-C covalent bond have been studied and quantified on their ground state by the means of geometry optimization, NBO analysis and calculation of their IR vibrations. IR fingerprints of the Ru-C bond have been found at 945 and 1113 cm(-1). In addition, this study confirmed and quantified the effects of N→C(-) substitution on the spectroscopic properties of the [RuN(5)C](+) complex: a broader and bathochromically-shifted absorption spectrum, a smaller ground-(3)MLCT energy gap and a highly energetic (3)MC state are the major characteristics of the carbon-containing monocationic complex.

Photophysical and electrochemical properties of polypyridine imine ruthenium(II) complexes: a comparative experimental and theoretical study

The photophysical and electrochemical properties of two ruthenium complexes formulated as [Ru(bpy)2LL′]2+ (bpy = 2,2′-bipyridine, LL′ = pyrim=phenylpyridin-2-ylmethylene-amine; and LL′ = Mes-dab = 1,4-dimesityl-1,4-diazabutadiene) have been investigated by a combined theoretical and experimental study. The UV/Vis absorption spectra of both complexes are dominated by absorption bands in the 400–600 region, which are assigned, by means of TD-DFT calculations, to metal-to-ligand charge transfer (MLCT) transitions, and the bands observed at 300 nm have a dominant intraligand character. The pyrim complex shows luminescence at both low and ambient temperature, whereas for the diaza Mes-dab complex no emission was observed in the visible region at all temperatures. Calculations showed that the presence of the Mes-dab ligand results in a strong decrease in the emission energy from the lowest triplet 3MLCT. As a result, we predict that the Mes-dab complex could be luminescent in the infrared region, while the pyrim complex emits in the visible region. Furthermore, in both cases, triplet metal-centered (3MC) states are inaccessible from the lowest triplet states, which is a requirement for efficient emission. Electrochemical data are typical of Ru(II) bipyridine complexes. DFT calculations, in the gas and the solvated phase, on the different oxidized and reduced species are consistent with metal-based oxidations and ligand-based reductions. The first reduction is always localized on the LL′ ligand. For the first time, the second reduction process was investigated for these kinds of complexes. It occurs at the same potential for the two complexes, as it corresponds to the reduction of the bipyridine ligands. The calculations match the experimental trend in electrochemical shifts.

Is photoisomerization required for NO photorelease in ruthenium nitrosyl complexes

AbstractThe factors that explain the competition between intramolecular NO linkage photoisomerization and NO photorelease in five ruthenium nitrosyl complexes were investigated. By applying DFT-based methods, it was possible to characterize the ground states and lowest triplet potential energy surfaces of these species, and to establish that both photoisomerization and photorelease processes can occur in the lowest triplet state of each species. This work highlights the crucial role of the sideways-bonded isomer, a metastable state also known as the MS2 isomer, in the photochemical loss of NO, while the results obtained also indicate that the population of the triplet state of this isomer is compulsory for both processes and show how photoisomerization and photorelease interfere.n Graphical AbstractIllustration of the crucial role of the 3MS2 state in the photoreactivities of ruthenium nitrosyl complexes

Ligand Selection in Ru-II Complexes for Direct One-Electron Photooxidation of Guanine: A Combined Computational and Experimental Study

Making the right ligand selection: DFT calculations of Gibbs energies for the one-electron photooxidation of guanine by six Ru(II)-polypyridine complexes are reported. The theoretical predictions are compared with new EPR spectra. Our theoretical calculations confirm the experimental observations that the direct photooxidation of guanine by [Ru(bpz)(3)](2+), [Ru(tap)(3)](2+), and [Ru(bpz)(2)(dppz)](2+) is thermodynamically favorable, but is unfavorable with [Ru(bpy)(3)](2+), [Ru(phen)(3)](2+), and [Ru(bpy)(2)(dppz)](2+) (see figure).

Combined theoretical and experimental studies of P3HT and PTB7 polymers for organic photodiodes

The polymer PTB7 is used in a fluorescence detection system for fabricating a bulk heterojunction (BHJ) organic photodiode as a photodetector. It is chosen and studied theoretically because of its suitable absorption bandwidth and electron donor efficiency when associated with PCBM in BHJ. However, in order to be sure of our theoretical prediction, we validated our method on the well-known P3HT. This is done by investigating experimentally and theoretically the UV-vis, Raman and photoluminescence (PL) spectra. As our experimental and theoretical results are in perfect agreement, we are confident on the photophysical properties of PTB7 predicted by our method.

Thermolysis biradical mechanisms in endoperoxides: A challenge for density functional theory?

We report a theoretical study of the thermal decomposition of benzene endoperoxide. A comparison between unrestricted density functional theory (UDFT) and highly correlated multireference ab initio methods has been carried out in order to assess the accuracy and reliability of UDFT to describe biradical mechanisms. The conclusion is that UDFT is a promising tool to describe the biradical mechanisms of endoperoxides. However, it can fail in the particular case of high multiconfigurational character associated with a rather weak biradical character, which happens in the first step of the stepwise cycloreversion mechanism of the prototype system studied, depending on the exchange–correlation functional used. Thus, caution has to be taken when arguing about the possible non-existence of biradical pathways with UDFT.

DFT rationalization of the room-temperature luminescence properties of Ru(bpy) 3 2+ and Ru(tpy) 2 2+ : 3 MLCT– 3 MC minimum energy path from NEB calculations and emission spectra from VRES calculations

Extensive experimental data covering 40xa0years of research are available on Ru(bpy)32+ and Ru(tpy)22+, which are the archetypes of inorganic photochemistry. The last decade has enabled computational chemists to tackle this topic through density functional theory and to shed some new light on our old friends. For the first time, this theoretical study maps the minimum energy path linking the 3MLCT (metal-to-ligand charge transfer) and the 3MC (metal-centred) states with the nudged elastic band method, also providing the calculation of the corresponding energy barrier. Remarkably, the obtained data are in very good agreement with the experimental activation energies reported from variable-temperature luminescence measurements. Calculation of vibrationally resolved electronic spectra is also in excellent agreement with the experimental emission maximum and bandshape of Ru(bpy)32+. Additionally, the 3MC–GS minimum energy crossing point was optimized for each complex. The combination of these data rationalizes the room-temperature luminescence of the bpy complex and non-luminescence of the tpy complex.

Revisiting the Vibrational and Optical Properties of P3HT : A Combined Experimental and Theoretical Study

We demonstrate that DFT-based calculations can provide straightforward means to analyze the effect of aggregation on the optical properties of regioregular P3HT oligomers of different lengths (up to 20-mers) and of bioligomers of 8-mers in two different conformations. Our conclusions substantially differ from those obtained previously by applying the exciton model. Indeed, analysis of Huang-Rhys factors has evidenced that two vibrational modes, a collective mode and an effective mode, are combined in the vibronic structure of the absorption spectrum of oligothiophene. Computed spectra match perfectly their experimental counterparts provided we consider that the oligomer and at least the five lowest excited states of bioligomers behave as absorbers, and that both oligomer and bioligomer contribute to the emission spectra. Study of the nature of the Franck-Condon excitation and optimization of the five lowest excited singlet states indicate that high (hot) excited states of the bioligomer may play an important role in the initiation of charge separation and highlight the importance to take into account the relaxation processes in the theoretical modeling of emission properties.