Abstract
The ground-state geometries, electronic structures, and electronic absorption spectra of symmetrical squaraine dyes SQ1–SQ4 were investigated using density functional theory and time-dependent DFT at the B3LYP level. The calculated geometries indicate that strong conjugation effects occur in the dyes. The highest occupied molecular orbital energy levels were calculated to be −4.95, −5.22, −5.09, and −5.06 eV, and the lowest unoccupied molecular orbital energies were −2.72, −3.05, −2.80, and −2.80 eV for SQ1–SQ4, respectively. Taking the conduction band energy of TiO2 into account, these data reveal the sensitized mechanism: the interfacial electron transfer between the semiconductor TiO2 electrode and the dye sensitizers SQ1–SQ4 are electron-injection processes from excited dyes to the semiconductor conduction band. The intense calculated absorption bands are assigned to π → π* transitions, which exhibit appreciable blue-shift compared with the experimental absorption maxima due to the inherent approximations in the TD-DFT.
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Acknowledgments
This work was supported by the Foundation of Wuhan University of Science and Engineering (No. 2009003 and 20073208), the Natural Science Foundation of Hubei Province (No. 2008CDB261), and the Key Project of Science and Technology Research of Ministry of Education (No. 208089). The authors gratefully wish to express their thanks to the reviewers for critically reviewing the manuscript and making important suggestions.
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Xu, J., Zhang, H., Wang, L. et al. DFT and TD-DFT studies on symmetrical squaraine dyes for nanocrystalline solar cells. Monatsh Chem 141, 549–555 (2010). https://doi.org/10.1007/s00706-010-0298-0
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DOI: https://doi.org/10.1007/s00706-010-0298-0