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Int. J. Mol. Sci. 2016, 17(4), 487; doi:10.3390/ijms17040487

Optical Absorption Spectra and Electronic Properties of Symmetric and Asymmetric Squaraine Dyes for Use in DSSC Solar Cells: DFT and TD-DFT Studies

Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah B.O. 208203, Saudi Arabia
Chemistry Department, Faculty of Science, Beni-Suef University, Beni-Suef 6251, Egypt
Max-Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany
Authors to whom correspondence should be addressed.
Academic Editors: Francesc Illas and Henry Chermette
Received: 26 December 2015 / Revised: 28 March 2016 / Accepted: 29 March 2016 / Published: 1 April 2016
(This article belongs to the Special Issue Chemical Bond and Bonding 2016)
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The electronic absorption spectra, ground-state geometries and electronic structures of symmetric and asymmetric squaraine dyes (SQD1–SQD4) were investigated using density functional theory (DFT) and time-dependent (TD-DFT) density functional theory at the B3LYP/6-311++G** level. The calculated ground-state geometries reveal pronounced conjugation in these dyes. Long-range corrected time dependent density functionals Perdew, Burke and Ernzerhof (PBE, PBE1PBE (PBE0)), and the exchange functional of Tao, Perdew, Staroverov, and Scuseria (TPSSh) with 6-311++G** basis set were employed to examine optical absorption properties. In an extensive comparison between the optical data and DFT benchmark calculations, the BEP functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic absorption spectra. The calculated energy values of lowest unoccupied molecular orbitals (LUMO) were 3.41, 3.19, 3.38 and 3.23 eV for SQD1, SQD2, SQD3, and SQD4, respectively. These values lie above the LUMO energy (−4.26 eV) of the conduction band of TiO2 nanoparticles indicating possible electron injection from the excited dyes to the conduction band of the TiO2 in dye-sensitized solar cells (DSSCs). Also, aromaticity computation for these dyes are in good agreement with the data obtained optically and geometrically with SQD4 as the highest aromatic structure. Based on the optimized molecular geometries, relative positions of the frontier orbitals, and the absorption maxima, we propose that these dyes are suitable components of photovoltaic DSSC devices. View Full-Text
Keywords: squaraine dyes; TD-DFT; electron transfer; optical properties; HOMO-LUMO gap squaraine dyes; TD-DFT; electron transfer; optical properties; HOMO-LUMO gap

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El-Shishtawy, R.M.; Elroby, S.A.; Asiri, A.M.; Müllen, K. Optical Absorption Spectra and Electronic Properties of Symmetric and Asymmetric Squaraine Dyes for Use in DSSC Solar Cells: DFT and TD-DFT Studies. Int. J. Mol. Sci. 2016, 17, 487.

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