What is the "best" atomic charge model to describe through-space charge-transfer excitations?

CEISAM, UMR CNRS 6230, BP 92208, Université de Nantes, 2, Rue de la Houssinière, 44322 Nantes, Cedex 3, France.
Physical Chemistry Chemical Physics (Impact Factor: 3.83). 03/2012; 14(16):5383-8. DOI: 10.1039/c2cp40261k
Source: PubMed

ABSTRACT We investigate the efficiency of several partial atomic charge models (Mulliken, Hirshfeld, Bader, Natural, Merz-Kollman and ChelpG) for investigating the through-space charge-transfer in push-pull organic compounds with Time-Dependent Density Functional Theory approaches. The results of these models are compared to benchmark values obtained by determining the difference of total densities between the ground and excited states. Both model push-pull oligomers and two classes of "real-life" organic dyes (indoline and diketopyrrolopyrrole) used as sensitisers in solar cell applications have been considered. Though the difference of dipole moments between the ground and excited states is reproduced by most approaches, no atomic charge model is fully satisfactory for reproducing the distance and amount of charge transferred that are provided by the density picture. Overall, the partitioning schemes fitting the electrostatic potential (e.g. Merz-Kollman) stand as the most consistent compromises in the framework of simulating through-space charge-transfer, whereas the other models tend to yield qualitatively inconsistent values.

1 Bookmark
  • [Show abstract] [Hide abstract]
    ABSTRACT: The design and preparation of an asymmetric ruthenium–diacetylide organometallic complex was successfully achieved to provide an original donor–π–[M]–π–acceptor architecture, in which [M] corresponds to the [Ru(dppe)2] (dppe: bisdiphenylphosphinoethane) metal fragment. The charge-transfer processes occurring upon photoexcitation of the push–pull metal–dialkynyl σ complex were investigated by combining experimental and theoretical data. The novel push–pull complex, appropriately end capped with an anchoring carboxylic acid function, was further adsorbed onto a semiconducting metal oxide porous thin film to serve as a photosensitizer in hybrid solar cells. The resulting photoactive material, when embedded in dye-sensitized solar cell devices, showed a good spectral response with a broad incident photon-to-current conversion efficiency profile and a power conversion efficiency that reached 7.3 %. Thus, this material paves the way to a new generation of organometallic chromophores for photovoltaic applications.
    Chemistry 04/2014; · 5.93 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Based on our recent report on a high overall conversion efficiency of the dye namely CCT3A exhibiting 96 % of the standard N719-based cell (Sudyoadsuk et al. in Eur J Org Chem, 23:5051–5063, 2013), a new series of metal-free organic donor–π–acceptor dyes are systematically further designed by an assistance of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. By taking carbazole–carbazole as a double-donor group and cyanoacrylic acid as an acceptor units, the π-linkers have been varied with different transporting moieties to investigate their potential performances in dye-sensitized solar cells (DSSCs) and evaluated through optimized geometries, charge distributions, electronic structures, simulated absorption spectra, and free energies of electron injection. The absorption spectrum of CCTA, one of our dyes in CCT3A series, was simulated by five different DFTs with various exchange–correlation functions to validate an appropriate functional prior to being employed as the functional of choice to investigate our new designed dyes. The long-range-corrected TD-CAM-B3LYP is found to provide the best results in predicting the λmax close to experimental data. The variation of π-linkers strongly affects the molecular orbital energy levels. The efficiencies of all dyes as sensitizers in DSSCs are also predicted by analyzing the important key parameters (the HOMO–LUMO energy gap (ΔH–L), dipole moment change (Δμ), distance of charge transfer upon excitation from ground to excited state (D CT), free energies of injection (ΔG inject), and light-harvesting efficiencies). Our results suggest that the two carbazole–carbazole-based dyes containing thieno [3,2-b]thiophene and benzothiadiazole as the π-linker exhibit higher efficiencies than the existing CCTA dye.
    Theoretical Chemistry Accounts 07/2014; 133(1523). · 2.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: DSSCs have been extensively investigated in the past decade, and the search for more efficient dyes for DSSCs remains challenging. In this work we discuss the influences of elongating π-spacers and rigidifying dithiophene on the performance of dithiafulvenyl (DTF)-based organic dyes using density functional theory (DFT) and time-dependent DFT methods. We show that systematically elongating the π-spacer of the DTF-2P dye by increasing the number of thiophene groups tends to red-shift the absorption peak and broaden the absorption range, thus improving the light-harvesting efficiency of DTF-2P-T and DTF-2P-2T. Furthermore, among the three dyes, DTF-2P-T would have the best performance because it performs nicely on the key parameters including the electron injection driving force (D), the light-harvesting efficiency (LHE), and the shift of the TiO2 conduction band (ΔEcb). In particular, DTF-2P-2T has a larger LHE despite the smaller D and ΔEcb compared with DTF-2P-T. Having realized the great merits of modification on π-spacers, afterwards, we designed a novel dye by rigidifying the dithiophene moiety of DTF-2P-2T. The resulting dye is proven to be very promising to challenge the conversion efficiency 8.29% of DTF-2P-T due to the improved ΔEcb and LHE. Our theoretical studies are expected to provide valuable insights into the molecular design of novel DTF-based dyes for the optimization of DSSC.
    Physical Chemistry Chemical Physics 04/2014; · 3.83 Impact Factor


Available from
Aug 26, 2014