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Wang T.-H.,National Tsing Hua University | Wang T.-H.,Nature and Science Group | Hsiao C.-H.,Chia Nan University of Pharmacy and Science | Chen S.-H.,Chia Nan University of Pharmacy and Science | And 2 more authors.
Polyhedron | Year: 2015

Graphical abstract Ru can be replaced by inexpensive Fe as the photo-sensitizer for DSSCs. ΔEL-H may be reduced by a low electronegative metal atom and a π-electron rich ligand. UV-Vis absorption intensity may be enhanced by a π-electron rich ligand as well as solvent. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) with the DZVP/DZVP2 all-electron mixed basis sets are used to study the related energies, structures, frontier molecular orbitals and UV-Vis spectra for [M(Tp)(PPh3)(Cl)(L)] (M = Ru and Fe; L = C3H4N2 and C13H11N). The related energies between the singlet state (low-spin) and nonet state (high-spin) for these complexes are reported. Because of the low related energies, these complexes are expected to be in the singlet state (low-spin). The calculated structural parameters for complexes 1 and 3 (Ru-based) are in very good agreement with the experimental values, and the geometries of complexes 2 and 4 (Fe-based) have been studied as well. The metal-ligand bond distances for the Fe-based complexes are predicted to be slightly shorter than those of the Ru-based complexes due to the small spatial extent of the 3d wave functions of the Fe atom. These complexes display a HOMO of metal d and π(Cl) orbitals in character, and the LUMO is contributed by metal d and π∗(PPh3) or π∗(C13H11N) orbitals. The HOMO-LUMO energy gap (ΔEL-H) can be reduced by a π-electron rich ligand (such as C13H11N) and a low electronegativity metal atom (such as Fe). A π-electron rich ligand (such as C13H11N) can increase the electron accepting ability, which leads to more electrons being pumped into the π∗(PPh3) and π∗(C13H11N) orbitals and results in a red-shift and intensity-enhanced absorption in the UV-Vis spectrum. The UV-Vis absorption intensity can be enhanced by solvent (such as CH3OH) as well as resulting in a blue-shift, which suggests that it is due to the polarizability and dielectric strength of the solvent. Owing to the low electronegativity of the Fe atom, a red-shift occurs in the UV-Vis spectra for complexes 2 and 4. The primary absorption features for complexes 1 and 3 are attributed to MLCT/LLCT transitions; on the other hand, a MLCT transition results in the primary absorption features for complexes 2 and 4. Our results show that Ru can be replaced by the inexpensive Fe as the photo-sensitizer. In addition, these Ru- and Fe-based complexes are good candidates for photo-sensitizers in DSSCs due to rich absorption bands and strong absorption intensities in the visible region. © 2015 Published by Elsevier Ltd. Source


Wang T.-H.,National Tsing Hua University | Wang T.-H.,Nature and Science Group | Hsiao C.-H.,Chia Nan University of Pharmacy and Science | Chen S.-H.,Chia Nan University of Pharmacy and Science | And 4 more authors.
Journal of Organometallic Chemistry | Year: 2015

In order to investigate whether Ru can be replaced by inexpensive Fe in photo-sensitizers for dye-sensitized solar cells (DSSCs), the differences in spin states, structures, frontier molecular orbitals and UV-vis spectroscopic properties of Ru- and Fe-based complexes are investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). These Ru- and Fe-based complexes are expected to be in singlet state (low-spin) because of low related energy. The calculated structural parameters for the [RuTp]-based complex are in very good agreement with experimental values; moreover, the geometries of the [RuCp]-, [FeTp]- and [FeCp]-based complexes have been predicted as well. The metal-ligand bond distances for the Fe-based complexes are predicted to be slightly shorter than these of the Ru-based complexes due to the smaller spatial extent of 3d wave functions of the Fe atom. These Ru- and Fe-based complexes display the HOMO with metal d-orbital and π(N3) orbital characters and the LUMO with metal d-orbital and π∗(C7H5N) orbital characters. The HOMO-LUMO energy gap (ΔEL-H) may be reduced by a low electronegativity of central metal atom, such as Fe. A low electronegativity metal atom (such as Fe) as well as an electron-rich ligand (such as Cp) may result in red shift for UV-vis spectra. Besides, the UV-vis absorption-enhanced by solvent, such as CH3OH, has been predicted. Our results show that Ru can be replaced by inexpensive Fe in photo-sensitizers for DSSCs. In addition, these Ru- and Fe-based complexes are good candidates for photo-sensitizers due to their absorption intensities and rich absorption bands in visible region. © 2015 Elsevier B.V. All rights reserved. Source

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