A general TDDFT procedure has been set up that accurately evaluates the UV/vis absorption spectra of a series of new conjugated metal-free organic dyes based on the triphenylamine (TPA) moiety, which have recently been developed for dye-sensitized solar cells (DSSCs). It turns out that the BHandH functional, combined with the 6-311+G(2d,2p) basis set, gives reliable auxochromic shifts when the bulk solvation effects are included in the model. Indeed, the theoretical procedure provides λmax with a mean absolute deviation limited to ∼0.1 eV only. In addition, we give insights into the geometrical and electronic structures of the dyes, and we unravel the structural modifications allowing to optimize the properties of TPA-based DSSCs. This investigation aims at improving the electron-injection process, as well as the light-harvesting efficiency (LHE) of the dyes. To this purpose, we considered a set of about 20 new dyes, and starting from the TPC-1 structure, the following modifications help to get better electron injection and light-harvesting properties: (i) the extension of the bridging group by addition of an ethylene subunit between the two phenyl groups (TPC-14); (ii) the 16-COOH, 15-OMe, 1a,6-diCN functionalization (TPC-18); (iii) moving the terminal cyano acceptor from the 16 to the 15 position, while introducing two −OMe functions in 11 and 13 positions and/or grafting two −CN groups in 1a and 6 positions on the TPA moiety (TPC-20). These specific modifications induce a maximal increase of the LHE and a more exoenergic free enthalpy of injection (−2.20 eV compared to −1.84 eV for TPC-1). Finally, TPC-23 (which results from the TPC-14/TPC-20 combination) shows an improvement of both the spectroscopic and energetic parameters. Moreover, the molecular topology analysis demonstrates that the coplanarity between the anchoring and the bridging unit is broken, that is, the positive charge is not directly in contact with the TiO2 surface, and the recombination reaction is therefore inhibited.

The structure and visible spectra of a large panel of thioindigo dyes and derivatives have been evaluated using a TD-PBE0/6-311+G(2d,p)//PBE0/6-311G(d,p) approach explicitly taking bulk solvent effects into account by means of the polarizable continuum model. The influence of the solvent characteristics, the trans-cis isomerization, and the chemical substitution on the benzene rings have been investigated. In addition, hemi-thioindigo dyes, thiazine-indigo, chromophore-like molecules, and selenoindigo have been considered. Though the relative oscillator strengths of the two allowed visible transitions in the nonplanar cis isomers are not always correctly reproduced by theory, the agreement between theoretical and experimental results is far above expectations. For the 170 cases studied, we obtained a mean unsigned error on the predicted lambda(max) limited to 6.9 nm or 0.03 eV, with only 6 (4) cases for which the difference exceeds 20 nm (0.10 eV). These errors are 1 order of magnitude smaller than what has previously been reported for indigoids. A linear correlation between the central double bond length and the lambda(max) has been established, while the bond length and vibrational frequency of the carbonyl groups do not correlate with the thioindigo color. The higher excitation energies of the cis conformers, compared to the trans structures, result from a less stabilized LUMO in the former case. Indeed, for cis thioindigo, the two electron-rich (in the excited state) carbonyl units lie close to each other.

The UV/visible spectra of a series of indigo derivatives have been evaluated by using ab initio methods. The combination of the Polarizable continuum model for estimating bulk solvent effects with the TD-B3LYP6-311 + G(2d,p)B3LYP6-311G(d,p) level of approximation, leads to an accurate description of the wavelength of maximum absorption of indigoids compounds. Using this procedure, we have assessed the effects of both the surroundings (solvent and solid state) and the substitution pattern. For the latter, we obtained a mean absolute deviation of only 7 nm (0.02 eV) compared to experiment, for a set of 86 molecules/solvents.

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We have computed the absorption spectra of a large series of anthraquinone dyes by using the time-dependent density functional theory (TD-DFT) for the excited-state calculations and the polarizable continuum model (PCM) for evaluating bulk solvent effects. On one hand, we compare the results obtained with the B3LYP and the PBE0 hybrid functionals, combined with different atomic basis sets. On the other hand, using multiple linear regression, we take advantage of the λmax predicted by these two functionals in order to reach the best agreement between theoretical estimates and experimental measurements. It turns out that 1. PBE0 provides more accurate results than B3LYP; in addition the average errors provided by the former are less basis set dependent. 2. Multiple linear regression provides excited state spectra in better agreement with experiment than any simple linear fit that could be performed. 3. Using our best fitting procedure, we obtained a mean absolute error of 6 nm for a set of 66 anthraquinones, with no deviations exceeding 25 nm. The related standard deviation, useful for predictions, is only 8 nm, i.e.,[Formula: see text] =[Formula: see text] ± 8 nm (or ±0.05 eV) for unknown anthraquinone compounds.