TD-DFT Assessment of Functionals for Optical 0–0 Transitions in Solvated Dyes

Using TD-DFT, we performed simulations of the adiabatic energies of 40 fluorescent molecules for which the experimental 0–0 energies in condensed phase are available. We used six hybrid functionals (B3LYP, PBE0, M06, M06-2X, CAM-B3LYP, and LC-PBE) that have been shown to provide accurate transition energies in previous TD-DFT assessments, selected two diffuse-containing basis sets, and applied the most recent models for estimating bulk solvation effects. In each case, the correction arising from the difference of zero-point vibrational energies between the ground and the excited states has been consistently determined. Basis set effects have also been carefully studied. It turned out that PBE0 and M06 are the most effective functionals in terms of average deviation (mean absolute error of 0.22–0.23 eV). However, both the M06-2X global hybrid that contains more <i>exact</i> exchange and the CAM-B3LYP range-separated hybrid significantly improve the consistency of the prediction for a relatively negligible degradation of the average error. In addition, we assessed (1) the cross-structure/spectra relationships, (2) the importance of solvent effects, and (3) the differences between adiabatic and vertical energies

Performance of an Optimally Tuned Range-Separated Hybrid Functional for 0–0 Electronic Excitation Energies

Using a set of 40 conjugated molecules, we assess the performance of an “optimally tuned” range-separated hybrid functional in reproducing the experimental 0–0 energies. The selected protocol accounts for the impact of solvation using a corrected linear-response continuum approach and vibrational corrections through calculations of the zero-point energies of both ground and excited-states and provides basis set converged data thanks to the systematic use of diffuse-containing atomic basis sets at all computational steps. It turns out that an optimally tuned long-range corrected hybrid form of the Perdew–Burke–Ernzerhof functional, LC-PBE*, delivers both the smallest mean absolute error (0.20 eV) and standard deviation (0.15 eV) of all tested approaches, while the obtained correlation (0.93) is large but remains slightly smaller than its M06-2X counterpart (0.95). In addition, the efficiency of two other recently developed exchange-correlation functionals, namely SOGGA11-X and ωB97X-D, has been determined in order to allow more complete comparisons with previously published data

A Database of Dispersion-Induction DI, Electrostatic ES, and Hydrogen Bonding α₁ and β₁ Solvent Parameters and Some Applications to the Multiparameter Correlation Analysis of Solvent Effects

For about 300 solvents, we propose a database of new solvent parameters describing empirically solute/solvent interactions: DI for dispersion and induction, ES for electrostatic interactions between permanent multipoles, α₁ for solute Lewis base/solvent Lewis acid interactions, and β₁ for solute hydrogen-bond donor/solvent hydrogen-bond acceptor interactions. The main advantage over previous parametrizations is the easiness of extension of this database to newly designed solvents, since only three probes, the betaine dye 30, 4-fluorophenol, and 4-fluoroanisole are required. These parameters can be entered into the linear solvation energy relationship <i>A</i> = <i>A</i>₀ + di­(DI) + <i>e</i>ES + <i>a</i>α₁ + <i>b</i>β₁ to predict a large number of varied physicochemical properties <i>A</i> and to rationalize the multiple intermolecular forces at the origin of solvent effects through a simple examination of the sign and magnitude of regression coefficients di, <i>e</i>, <i>a</i>, and <i>b</i>. Such a rationalization is illustrated for conformational and tautomeric equilibria and is supported by quantum-mechanical calculations

Choosing a Functional for Computing Absorption and Fluorescence Band Shapes with TD-DFT

The band shapes corresponding to both the absorption and emission spectra of a set of 20 representative conjugated molecules, including recently synthesized structures, have been simulated with a Time-Dependent Density Functional Theory model including diffuse atomic orbitals and accounting for bulk solvent effects. Six hybrid functionals, including two range-separated hybrids (B3LYP, PBE0, M06, M06-2X, CAM-B3LYP, and LC-PBE) have been assessed in light of the experimental band shapes obtained for these conjugated compounds. Basis set and integration grid effects have also been evaluated. It turned out that all tested functionals but LC-PBE reproduce the main experimental features for both absorption and fluorescence, though the average errors are significantly larger for the latter phenomena. No single functional stands out as the most accurate for all aspects, but B3LYP yields the smallest mean absolute deviation. On the other hand, M06-2X could be a valuable compromise for excited-states as it reproduces the 0–0 energies and also gives reasonable band shapes. The typical mean absolute deviations between the relative positions of the experimental and theoretical peaks in the vibrationally resolved spectra are ca. 100 cm^–1 for absorption and 250 cm^–1 for emission. In the same time, the relative intensities of the different maxima are reproduced by TD-DFT with a ca. 10–15% accuracy

Electronic Band Shapes Calculated with Optimally Tuned Range-Separated Hybrid Functionals

Using a set of 20 organic molecules, we assess the accuracy of both the absorption and emission band shapes obtained by two optimally tuned range-separated hybrid functionals possessing 0% (LC-PBE*) and 25% (LC-PBE0*) of short-range exact exchange as well as by four other hybrid functionals including or not dispersion and long-range corrections (APF-D, PBE0-1/3, SOGGA11-X, and ωB97X-D). The band topologies are compared to experimental data and to previous time-dependent density functional theory calculations. It turns out that both optimally tuned functionals vastly improve the vibronic band shapes obtained with the non-tuned LC-PBE approach but, statistically, do not yield more accurate topologies than standard hybrid functionals. In other words, optimal tuning allows to obtain more accurate excited-state energies without degrading the description of band shapes. In addition, the LC-PBE0* 0–0 energies have been determined for a set of 40 compounds, and it is shown that the results are, on average, less accurate than those obtained by LC-PBE* for the same panel of molecules. The correlation between the optimal range-separation parameters determined for LC-PBE* and LC-PBE0* is discussed as well

Determination of a Solvent Hydrogen-Bond Acidity Scale by Means of the Solvatochromism of Pyridinium‑<i>N</i>‑phenolate Betaine Dye 30 and PCM-TD-DFT Calculations

Empirical parameters of solvents describing their hydrogen-bond (HB) acidity (e.g., the Kamlet–Taft α parameter) are often difficult to determine for new solvents because they are not directly related to a single definition process. Here, we propose a simple method based on one probe, the betaine dye <b>30</b>, and one reference process, the solvatochromism of this dye, measured by its first electronic transition energy, <i>E</i>_T(30). These <i>E</i>_T(30) values are calculated within the time-dependent density functional theory framework, using a polarizable continuum solvent model (PCM). The part of <i>E</i>_T(30) values that is not included in the PCM calculation is taken as the HB component of the measured <i>E</i>_T(30) values, allowing us to deduce a solvent HB acidity parameter α₁. The validity of this simple model is assessed by good linear correlations between α₁ and a variety of solute properties mainly depending on the solvent’s HB acidity. The quality of fit observed with α₁ is at least comparable with that obtained by previous solvent HB acidity scales. The simplicity of our method is illustrated by the determination of α₁ and of its companion, the electrostatic solvent parameter <i>ES</i>, for some new green solvents derived from glycerol

1‑Oxo‑1<i>H</i>‑phenalene-2,3-dicarbonitrile Heteroaromatic Scaffold: Revised Structure and Mechanistic Studies

Synthesis of the originally proposed 8-oxo-8<i>H</i>-acenaphtho­[1,2-<i>b</i>]­pyrrol-9-carbonitrile led to a structural revision, and the product has now been identified as unknown compound 1-oxo-1<i>H</i>-phenalene-2,3-dicarbonitrile. The structural assignment was corroborated by detailed NMR studies and unambiguously confirmed by X-ray diffraction. A mechanism is proposed to explain the formation of this original heterocyclic scaffold. In addition, some new chemical transformations involving this compound are presented

1‑Oxo‑1<i>H</i>‑phenalene-2,3-dicarbonitrile Heteroaromatic Scaffold: Revised Structure and Mechanistic Studies

Synthesis of the originally proposed 8-oxo-8<i>H</i>-acenaphtho­[1,2-<i>b</i>]­pyrrol-9-carbonitrile led to a structural revision, and the product has now been identified as unknown compound 1-oxo-1<i>H</i>-phenalene-2,3-dicarbonitrile. The structural assignment was corroborated by detailed NMR studies and unambiguously confirmed by X-ray diffraction. A mechanism is proposed to explain the formation of this original heterocyclic scaffold. In addition, some new chemical transformations involving this compound are presented

Palladium-Catalyzed Direct Arylation of Luminescent Bis-Cyclometalated Iridium(III) Complexes Incorporating <i>C</i>^<i>N-</i> or <i>O</i>^<i>O</i>‑Coordinating Thiophene-Based Ligands: an Efficient Method for Color Tuning

We report the palladium-catalyzed direct 5-arylation of both metalated and nonmetalated thiophene moieties of iridium complexes <b>2</b>, <b>3</b>, and <b>4</b> with aryl halides via C–H bond functionalization. This method opens new routes to varieties of Ir complexes in only one step, allowing easy modification of the nature of the ligand. The photophysical properties of the new functionalized complexes have been studied by means of absorption and emission spectroscopy. The extension of the π-conjugated system induces a bathochromic and hyperchromic shift of the absorption spectra, an effect reproduced by first principle calculations. Indeed, the bathochromic shifts are related to a more delocalized nature of the excited-states. All complexes are photoluminescent in the red region of the spectrum. This study establishes that arylation of the thienyl ring affects strongly the electronic properties of the resulting complexes, even when the thienyl ring is remote and not directly metalated to the iridium center, as in the thienyltrifluoroacetonate complex <b>4</b>

Palladium-Catalyzed Direct Arylation of Luminescent Bis-Cyclometalated Iridium(III) Complexes Incorporating <i>C</i>^<i>N-</i> or <i>O</i>^<i>O</i>‑Coordinating Thiophene-Based Ligands: an Efficient Method for Color Tuning

We report the palladium-catalyzed direct 5-arylation of both metalated and nonmetalated thiophene moieties of iridium complexes <b>2</b>, <b>3</b>, and <b>4</b> with aryl halides via C–H bond functionalization. This method opens new routes to varieties of Ir complexes in only one step, allowing easy modification of the nature of the ligand. The photophysical properties of the new functionalized complexes have been studied by means of absorption and emission spectroscopy. The extension of the π-conjugated system induces a bathochromic and hyperchromic shift of the absorption spectra, an effect reproduced by first principle calculations. Indeed, the bathochromic shifts are related to a more delocalized nature of the excited-states. All complexes are photoluminescent in the red region of the spectrum. This study establishes that arylation of the thienyl ring affects strongly the electronic properties of the resulting complexes, even when the thienyl ring is remote and not directly metalated to the iridium center, as in the thienyltrifluoroacetonate complex <b>4</b>