Cloé Azarias

Bethe-Salpeter study of cationic dyes: Comparisons with ADC(2) and TD-DFT

We present a theoretical investigation of the excited-state properties of a large series of structurally diverse arylcarbonium derivatives that are known to be challenging for theoretical models. More specifically, we compare the pros and cons of TD-DFT (TD-M06-2X), ADC(2), and BSE/GW approaches for a large panel of compounds, using two different solvent models. Both 0-0 and vertical transition energies are considered and compared to the experimental values. All approaches reasonably reproduce the auxochromic and acidochromic shifts, although in most cases both TD-DFT and BSE/GW return larger correlation with experimental values than ADC(2) for these shifts. In contrast, the absolute transition energies obtained with ADC(2) tend to be closer to the measurements, TD-DFT using the M06-2X functional largely overestimating the experimental references (by ca. 0.5 eV), and BSE/GW providing intermediate values. In addition, we show that the selected solvent model has a significant impact on the results, the corrected linear-response approach providing larger transition energies than its linear-response counterpart.

Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption

Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (σ2PA ) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, ≈18 D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900 nm. The expansion via a triple bond resulted in the largest peak value, σ2PA =770 GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0 →S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7 D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state.

Combined TD-DFT-SOS-CIS(D) Study of BOPHY Derivatives with Potential Application in Biosensing

A set of 13 bis(difluoroboron)-1,2-bis((pyrrol-2-yl)methylene)hydrazine (BOPHY) dyes is studied through a hybrid time-dependent density functional theory (TD-DFT)-scaled opposite spin-configuration interaction singles with a double correction [SOS-CIS(D)] approach accounting for solvent effects, to shed light onto the structure-property relationships of these recently developed chromophores. In the first step, we calculate the absorption-fluorescence crossing points with refined TD-DFT models considering the influences of both vibrational and solvent contributions. We found that the systematic overestimation of the 0-0 energies is effectively reduced by combining polarizable continuum model-TD-DFT with a scaled opposite spin-configuration interaction singles with a double correction [SOS-CIS(D)]. Next, for a representative system, the vibrationally resolved spectrum within the harmonic approximation is computed on the basis of TD-DFT vibrational signatures and an excellent match with experiment is found. Finally, the influence of different lateral groups on the spectroscopic properties is rationalized by investigating charge transfer parameters and examining electronic density difference maps. It is found that one can tune the position of the absorption/emission maxima by a judicious choice of the lateral substituents or by using π-extended segments. The largest absorption and emission wavelengths as well as the largest Stokes shifts are obtained for BOPHYs containing strong electron-donor dimethylaminophenyl groups attached to the α-positions of the pyrrole units through vinyl linkers, making these chromophores promising candidates for bioluminescence applications.

Structural and Optical Properties of Subporphyrinoids: A TD-DFT Study

Using ab initio approaches accounting for environmental effects, we investigate the ground- and excited-state properties of four subporphyrinoids: subporphyrin, subporphyrazine, tribenzosubporphyrin, and subphthalocyanine. We first show that the selected level of theory, that is DFT(PBE0), is able to reproduce the structure and NMR spectra of all compounds. The aromaticity of these four macrocyclic entities are next quantified and it is showed that these bowl-shape induced molecules present very strong aromatic characters. Next we analyze the spectral signatures of all four compounds using an approach going beyond the vertical approximation. The 0-0 energies are reproduced with a mean absolute deviation smaller than 0.1 eV, and the very good agreement obtained between experimental and theoretical band shapes allows us to unravel the vibronic contributions responsible to the specific band shapes of these subporphyrinoids. Finally, we investigate a large series of substituted subporphyrins, demonstrate the quality of the trends that are obtained with theory and design new compounds presenting red-shifted optical bands.

Elucidating the Nature of Carbazole–Porphyrinoids with First-Principle Approaches

Carbazole-porphyrinoids are [20]porphyrins that can be oxidized to the so-called porphyrin state, inducing a huge shift of the main absorption band from the UV-visible to the infrared region. In this study, we focus on the compound synthesized by Arnold and co-workers [ Arnold , L. ; Baumgarten , M. ; Müllen , K. A. Chem. Commun. , 2012 , 48 , 9640 - 9642 ], where the two pyrroline units of a porphyrin are replaced with carbazole moieties. Due to the poor stability of these macrocycles, the nature of the oxidation product could not be definitively ascertained experimentally. In that framework, with the help of ab initio approaches, we investigate the structure, the stability, the aromaticity, and the spectroscopic signatures of both the nonoxidized compound and a series of possible oxidation products. Thanks to vibronic simulations, we obtain insights into the nature of the oxidized macrocycle.

Controlling the canonical/zwitterionic balance through intramolecular proton transfer: a strategy for vapochromism

A series of N-substituted diamino-benzoquinone diimines featuring tunable aryl electron-withdrawing functions were synthesized. For the first time, the subtle variation of electronic richness allows controlling the canonical vs. zwitterionic equilibrium through the tuning of an intramolecular proton transfer. The establishment of a ground-state zwitterionic electronic structure, in lieu of the canonical one, within a monocyclic architecture is evidenced by the X-ray structure of one compound (4) and the telltale absorption spectra of the whole series that display an unexpected signature at low energy (ca. 700 nm). The evolution of this peculiar band is concomitant with the electron-withdrawing strength of the aryl substituents and theoretical calculations highlight that this band can be attributed to a charge transfer transition from the anionic cyanine towards the cationic cyanine. Finally, such a color change is advantageously used for the rapid and naked-eye detection of N,N-dimethylformamide using 3a as a vapochromic material. This latter experiment shows the first case of intramolecular solid-state proton transfer occurring in a polar environment.

Theoretical spectroscopy of a NIR-absorbing benziphthalocyanine dye

Benziphthalocyanines are (Yanai et al. in Chem Phys Lett 393:51–57, 2004) phthalocyanines in which one isoindoline unit has been replaced by a phenyl ring. In this study, we focus on a macrocycle of this family recently synthesized by Uchiyama and co-workers (Toriumi et al. Angew Chem Int Ed 53:7814–7818, 2014), and composed of three indoline units (substituted with 2,6-diisopropylphenyl-oxy groups) and one resorcinol unit. We aim at characterizing the possible tautomers to evaluate whether this compound might exist as a mixture of several forms or not. To reach our goals, we use state-of-the-art ab initio theories, i.e., Time-Dependent Density Functional Theory coupled with a refined solvation model (the Polarizable Continuum Model) as well as post-Hartree Fock approaches. We first investigate the stability, the structure and the aromaticity of the possible tautomers before analyzing their spectroscopic signatures. Using an approach going beyond the vertical approximation, we compare experimental and theoretical 0–0 energies and band shapes. This study allows us to point out the dominant presence of the quinoidal form as well as to unravel the vibronic contributions responsible for the specific shape of the optical spectrum.

Straightforward metal-free synthesis of an azacalix[6]arene forming a host–guest complex with fullerene C60

Electronic Supplementary Information (ESI) available: Details of the TD-DFT calculations, NMR spectra of 3b and 4b, preliminary spectrophotometric titration experiments. See a Contrasting with the well mastered azacalix[4]arene, the synthesis and characterization of azacalix[6]arene derivatives remains a challenge for chemists. In this framework, bulky n-octylamino groups appended on the 1,3-meta-diaminobenzene 2b can lead to the concomittant and straightforward one-pot formation of the azacalix[6]arene 4b and of the thermodynamically favoured azacalix[4]arene 3b through simple consecutive nucleophlic aromatic substitutions. The conformations of 3b and 4b were studied in solution and in the solid state using their molecular structures, their NMR and UV-visible spectra combined with first principle TD-DFT calculations. Preliminay solution experiments show that 4b can form a 1:1 host-guest complex with C60.