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A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) has been performed to study a Ruthenium polypyridyl complex named cis-dithiocyanatobis-(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) (N3) sensitized TiO 2 solar cell including dye excitations and electronic injection. Three binding structures of N3 anchored to a TiO 2 nanoparticle (TiO 2 ) 38 have been adopted. The electronic structures and optical properties of N3 dye in gas phase, in solutions (with the explicit and implicit solvent models), and interfaced with TiO 2 have been calculated. The hybrid DFT exchange-correlation (XC) functional B3LYP and PBE0, the newly-modified PBE0 functional PBE0-1/3, and the long-range corrected DFT (LRC-DFT) XC functional Cam-B3LYP have been applied. It is found that both the DFT XC functionals and molecular environments play a crucial role on molecular properties, which affect both the spectral lineshapes and peak positions. Coupled with PCM model, TD-PBE0-1/3 produces the best result compared with the experimental spectrum of N3 in CH 2 Cl 2 , TD-B3LYP slightly underestimates the excitation energies, and TD-Cam-B3LYP overestimates the excitation energies of 0.4–0.5 eV. As the solvent polarity increases, the electronic absorption spectra of N3 dye blue shift. The absorption manners of N3 anchored to (TiO 2 ) 38 affect the electronic excitations, leading to different electronic injection pathways. Two of three anchoring manners favor the interfacial electronic transfer. In the end, three possible electronic injection pathways from the different parts of the excited dye to TiO 2 nanoparticle have been suggested, indicating the different timescales of electron injections. [ABSTRACT FROM AUTHOR]

Abstract: We perform the time-dependent long-range corrected density functional theory (TD-LRC-DFT) studies on the electron excitation of Bacteriochlorophyll (BChl) and its assembly in two peripheral light-harvesting complexes (known as LH2) from purple bacteria. It is found that LRC-DFT gives a more reasonable description to the excitation energies and the energy spacings of both the single BChl pigment and its assembly than the conventional hybrid functionals, such as B3LYP and PBE0. The long-range correction to the conventional DFT exchange functionals is essential to correctly describe their electron excitation. For a single BChl pigment, both Q y and Q x excitations are highly delocalized, and Q y excitation involves obvious metal-to-ligand intramolecular charge-transfer character, and thus, it is more sensitive to xc functionals and solutions. From the results of three typical BChl pairs of LH2 complex, it is found that localized intramolecular Frenkel excitons (FEs) dominate the energy transfer process. Slight mixing between FEs and intermolecular charge-transfer excitons (CTEs) is observed in the pair 1α1β of 850 ring. The conventional functionals, such as B3LYP, underestimate intermolecular CTE energies, lay CTEs close to both Q y and Q x states. In this case, the mixing degree between the intramolecular FEs and intermolecular CTEs increases, which induces much narrow energy spacing between two lowest excited states of the pair 1α1β. It is thus incorrect to use the energy splitting of 1α1β resulted from B3LYP as the scalar to estimate the excitonic coupling and site energies as well. [ABSTRACT FROM AUTHOR]