Theoretical Investigation of Structural and Electronic Properties of Ruthenium Azopyridine Complexes Dyes for Photovoltaic Applications by Using DFT and TD-DFT Methods

In this work, a series of ruthenium azopyridine complexes was studied theoretically as a sensitizer in Dye Sensitized Solar Cells (DSSCs) using density functional theory (DFT) and time-dependent DFT (TD-DFT). These dyes derive from ruthenium azopyridine complex RuCl2(Azpy)2 considered as the reference by grafting an anchoring group (-COOH). Hens, 4-Hmazpy, 5-Hmazpy and O-Hazpy ligands as well as Azpy were studied. For the four ligands, 20 isomers expected are studied. In order to explore their photoelectrical properties, the ground state and excited state properties of the isolated dyes have been calculated at B3LYP/LANL2DZ level. And the same work was done with the dye RuCl2(5Hmazpy)2 in interaction with titanium dioxide. Comparing to N3, the key parameters including the light harvesting efficiency (LHE), the electron injection driving force ΔGinject , the regeneration driving force ΔGregen , the open circuit voltage VOC, the life time τ and adsorption energy were all scrutinized in detail. It results from this calculation that the ruthenium azopyridine complexes can be used as sensitizer in DSSCs. This work has highlighted the predictive and the guiding role of the theoretical approach in the design and the conception of new dyes for solar cells

Theoretical Studies of the Chemical Reactivity of a Series of Coumarin Derivatives by the Density Functional Theory

The global descriptors of reactivity such as HOMO and LUMO energies, chemical hardness, electrophilicity, softness and dipole moment are theoretically determined for five coumarin derivatives in this paper. The analysis of the determined descriptors allows us to classify the studied molecules according to their reactivities. Thus, compound M3 is qualified to be the most reactive and the least stable with 3.933 eV as its gap energy ΔEgap. It is at the same time the softest, the best electron donor, the most electrophilic and the most polar molecule. The study of thermodynamic parameters shows that all the reactions of formation of studied coumarin derivatives are exothermic and spontaneous with less disorder. Furthermore, Hirschfield population analysis was carried out in order to locate the reactive sites, that are assumed to be the electrophilic and nucleophilic sites of the molecules. It appears that all the reactive sites are located on carbon atoms except those of molecule M3 which are located on oxygen atoms. Compounds M1 and M2 have the same electrophilic site (C15) and the same nucleophilic site (C13) thereby showing that the methyl group does not have any influence on the reactive site. The electrophilic site of the molecule M3 is located on both the identical oxygen atoms O33 and O34 while its nucleophilic site is located on the oxygen atoms O12. The electrophilic sites of compound M4 and M5 are the same and it is located on carbon atom(C11) while the nucleophilic site is located on carbon atom C23 for molecule M4. Concerning the nucleophilic sites of molecule M5 it is located on carbon atom C20. The difference nucleophilic reactive site may be due to the conjugation of activity of both fluorine atom and methyl group on the M5