Blanc SIMI 7 - Sciences de l'information, de la matière et de l'ingénierie : Chimie moléculaire, organique, de coordination, catalyse et chimie biologique

Photophysics of phosphorus-ligands ruthenium and iridium complexes : joint experimental and theoretical investigations – PhosphoRuIr

Organophosphorus compounds and photosensitive metals for photovoltaïcs : joint experimental and theoretical investigations

Solar energy conversion into electrical energy is one of the great challenges of our society. Third generation dye-sensitized solar cells possess the advantages of implementing low-cost manufacturing processes and use «low« purity component. For this technology to be commercially feasible, it is necessary to increase the range of absorption wavelength of the dye to the near and far infrared and to lower very significantly the cost. It is therefore crucial to control the properties of the dye.

Organophosphorus complexes to fine tune electronic transfer of photosensitive dyes for third generation dye-sensitized solar cells

In order to expand the range of absorption wavelength of the dye to increase its efficiency and to lower very significantly its cost in 3rd generation solar cell devices, we chose to coordinate organophosphorus ligands, largely neglected in this field, on polypyridyl ruthenium complexes. The polypyridyl ruthenium fragments were used as models. The performances of our studied complexes were compared to those of polypyridyl ruthenium dyes already described in the literature. The knowledge gained in this project on polypyridyl ruthenium complexes, used as a reference in this study, could be transposed to efficient and much cheaper metallic dyes, ignored until now, such as iron complexes.

Our project is based on joint experimental and theoretical studies Throughout this project, a bibliography work sleep was performed. Our investigations have required a major work of synthesis and optimization . The electrochemical analysis allow to determine the ground state energy gap between the first oxidation and first reduction potentials of the studied complexes. The energy of the metal-ligand transition was recorded by UV-visible absorption spectroscopy. Both techniques quantitatively report the intimate energy parameters of each dye. In the excited state, we used the emission phenomenon as a probe to assess the effect of phosphorus ligands on the photophysical properties of the corresponding polypyridyl ruthenium complexes. These experimental approaches are supported by advanced theoretical calculations on both ground and excited states of our complexes. Investigations of the free energy profile between the excited states of our organophosphorus ruthenium complexes were performed through highly challenging calculations. This theoretical approach of the excited states rationalized the influence of the effects of organophosphorus and diazabutadiene nitrogen type ligands on the electron tranfer properties of our studied ruthenium polypyridyl complexes.

Our investigations revealed a very good correlation between :
(i) the ground and excited state properties of our complexes determined experimentally and
(ii) the ground state calculations and the excited state free energy profile theoretical calculations.

Our joint experimental and theoretical results demonstrated that organophosphorus ligands and diazabutadiene nitrogen type ligands coordinated on polypyridyl ruthenium metallic fragments, used as model, allow to modulate their electrochemical and photophysical properties over a wide range unmatched by other ligands.

We also succeeded to identify and characterize unusual compounds that are stable radical photosensitive metal complexes.

The knowledge gained in this project allow us to look to translate our findings to low cost metals such as iron to be integrated as a dye in a cheap and efficient photovoltaic device . This technology is compatible with sustainable development.

Our unexpected preliminary results in the preparation and identification of stable photosensitive organophosphorus ruthenium radical complexes open a new field of fundamental research in the domain of electron transfer.

Several international and national oral communications have been presented on the results we recorded on the project PhosphoRuIr.
To get an insight on the effect of diazabutadiene ligands on the photophysical properties of model ruthenium complexes, theoretical (Inorg. Chem. 2010) followed by joint experimental/theoretical (New J. Chem. 2012) studies were investigated. The remarquable properties of phosphoryl ruthenium complexes are described in Inorg. Chem. 2014 and New J. Chem. 2013. Theoretical investigation of phosphinidene oxide polypyridine ruthenium complexes appeared in J. Phys. Chem. A 2013.
Several other publication related to this project are under progress.

References :

T. Guillon, M. Boggio-Pasqua, F. Alary, J.-L. Heully, E. Lebon, P. Sutra, A. Igau
Inorg. Chem. 2010, 49, 8862.

R. E. Piau, T. Guillon, E. Lebon, N. Perrot, F. Alary, M. Boggio-Pasqua, J.-L. Heully, A. Juris, P. Sutra, A. Igau
New J. Chem. 2012, 36, 2484.

R. Sylvain, L. Vendier, C. Bijani, A. Santoro, F. Puntoriero, S. Campagna, P. Sutra, A. Igau
NewJ.Chem. 2013, 37, 3543.

O. P. J. Vieuxmaire, R. E. Piau, F. Alary, J.-L. Heully, P. Sutra, A. Igau, M. Boggio-Pasqua
J. Phys. Chem. A 2013; 117, 12821.

E. Lebon, R. Sylvain, R. E. Piau, C. Lanthony, J. Pilme´, P. Sutra, M. Boggio-Pasqua, J.-L. Heully, F. Alary, A. Juris, A. Igau
Inorg. Chem. 2014, 53, 1946.

In the respect of sustainable development, among the possible alternatives to fossile fuels energies, conversion between electrical and light energies constitutes an ambitious challenge. Despite some successful examples, much more fundamental knowledge is required to improve the yields of conversion. Dye-Sensitized Solar Cells (DSSCs) use the electronic properties of the ground and excited states of transition metal complexes as converting agent of sunlight into electricity. Traditional lighting systems operate electrical to light conversion with low efficiencies which induce high power consumption. “Organo-metallic” Light-Emitting Diodes (OLEDs) are expected to be one of the most promising candidates to increase the yields of electrical to light conversion. The technology of OLEDs is based on the luminescence properties of emissive agents. Transition metal complexes constitute one of the best suited luminescent compounds as their photophysical properties can be tuned through the nature of the ligands coordinated to the metal.
The synthesis and examination of compounds containing phosphorus atom in low-coordinated bonding environments have been a focus of modern main group chemistry. Cationic, anionic, and neutral P-bonded phosphorus derivatives with low coordination number exhibit a large range of potential bonding modes to a metal. Despite the huge amounts of photophysical studies on luminescent d6 transition metal complexes, very few examples with P-coordinated phosphorus ligands have been reported. P-bonded phosphorus derivatives with low coordination number are therefore good candidates to tune the electronic and photophysical properties of luminescent complexes.
Our project, divided in four tasks, is directed toward a systematic combined experimental and theoretical approach of the parameters that can control the electronic and photophysical properties of transition metal complexes incorporating low-coordinated phosphorus ligands. We selected ruthenium as a model metal due to the extensive literature on its photophysics. The ruthenium fragment archetypes we will study for coordination of phosphorus ligands are [Ru(tpy)(bpy)]2+ and [Ru(bpy)2]2+.
In preliminary experimental studies, we observed room temperature luminescence with functionalized P-bonded phosphine and R2P(O)- type ligands on ruthenium [Ru(tpy)(bpy)]2+ fragment. The first task of this project consists in the updated bibliographic study of experimental work and theoretical calculations of the ground and excited states of d6 complexes. Task 2 concentrates on experimental and theoretical studies of ligand field effect of low-coordinated phosphorus ligands (phosphenium R2P+, phosphido R2P-, and phosphinidene RP) on the archetype [Ru(tpy)(bpy)]2+ and [Ru(bpy)2]2+ fragments. The low-coordinated phosphorus ligands are expected to enhance the splitting of the d orbitals of the metal and thus increase the 3MC energy level. Task 3 will be based on the stabilization of a low-lying 3MLCT using pi-acceptor ligands. In this aim, starting from the complexes which gave the best emission properties in Task 2, we will substitute the conventional terpyridine and bipyridine N-coordinated ligands by bis(2-pyridyl)-1,3,5-triazines derivatives (trz) and/or acyclic alpha-diimine ligands (dim) as stronger pi-acceptor ligands. Theoretical computations will be of great support in order to rationalize and predict the ligand field effects around the ruthenium metal center. Finally, we will combine, in Task 4, the ligands which gave the most efficient ligand field effects on 3MC and 3MLCT with iridium(III). The aim of this task is to prepare new original room temperature luminescent complexes with long-lived excited states.

Project coordination

Alain IGAU (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE MIDI-PYRENEES) – alain.igau@lcc-toulouse.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LCPQ CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE MIDI-PYRENEES
LCC CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE MIDI-PYRENEES

Help of the ANR 389,999 euros
Beginning and duration of the scientific project: - 48 Months

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