Author(s): Freja E Storm, Thorsten Hansen and Kurt V Mikkelsen*
In this article a Density Functional Theory (DFT) description of derivatives of boron-subphthalocyanines (SubPc) is investigated. Investigated structures are peripherally functionalized derivatives. It is shown that the generalized gradient functional results of the geometry dier from the geometries found with the hybrid functionals, but the deviation is only of the order of a few percent of the total bond lengths for any of the investigated functionals. A linear response investigation is also used, where experimental UV-Vis results are compared with computational results. These investigations show that none of the investigated functionals are able to compute both peak position of the Q and soret band, but that the functional CAM-B3LYP does give results that are qualitatively useful, as this is the functional that comes closest to the correct separation of the peaks. A basis set investigation shows little dierence in results within the same functional. To compare results with experimental data, vibornic coupling eects are included using the Franck-Condon, Hertzberg-Teller approximation, and a close resemblance of CAM-B3LYP and experimental results are found. Linear response results found with the functionals BP86, B3LYP and CAM-B3LYP are also reported for 7 SubPc derivatives, and these show, as has been reported earlier, that peripheral functionalization has inuence on the frequency and intensity of absorption. These results also show a discrepancy between hybrid functionals and BP86, where BP86 predicts transitions at much lower energies - 300 nm red-shifted compared to the linear response result found with B3LYP and CAM-B3LYP. This is as expected for the treatment of charge transfer states with a generalized gradient functional and illustrates why BP86, though suitable for describing the position of the Q-band for unfunctionalized SubPc, might not be the best density functional to utilize when investigating SubPc based molecular dyads and triads.
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