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

International audienceWe 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

Central substitution of azacalixphyrins: a strategy towards acidochromic NIR dyes

International audienceAzacalixphyrin derivatives constitute one of the most intriguing class of macrocyclic compounds. Indeed, these isostructural and isoelectronic analogues of porphyrins intensively absorb light up to the near infrared region, exist in several tautomeric forms and present a bis-zwitterionic structure, with a central dianionic core surrounded by positively-charged trimethine cyanines. However, control of the position of the absorption bands of azacalixphyrin remains an important challenge, as the experimental attempts reported to date have led to very modest auxochromic shifts only. Inspired by previous work demonstrating that the optical signatures of cyanines can be strongly modified by using central substituents, we have evaluated the validity of this strategy for azacalixphyrin considering several substituents positioned in symmetric or asymmetric manners around the core and linked through both single and double bonds, as well as several protonation states of the macrocycles. It turns out that bromine and dimethylamino substituents have a negligible or weak impact on the optical properties of azacalixphyrins with maximal redshifts smaller than 0.10 eV. The imino substitution induces strong geometrical deformations that counterbalance the electronic effects leading to rather modest variations of the optical signatures. In contrast, for keto-substituted macrocycles, electronic effects dominate and very strong acidochromic shifts are predicted with absorption wavelengths going from 811 to 1095 nm upon double deprotonation

Modeling excitation energy transfer in multi-BODIPY architectures

The excitation energy transfer (EET) allowing the concentration of the energy has been investigated in several multi-BODIPY architectures with the help of an approach coupling time dependent density functional theory to an implicit solvation scheme, the polarizable continuum model. We have first considered several strategies to compute the electronic coupling in a dyad varying the size of the donor/acceptor units, the bridge, the geometries and conformations. We have next studied the electronic coupling in three different architectures for which the EET rate constants have been experimentally measured both from luminescence and transient absorption data and from Förster theory. A good agreement with experimental values was obtained. Finally, in an effort to further improve these systems, we have designed several series of BODIPY triads, investigating the effect of acidochromism, core modifications, the position of the linkage and chemical substitutions on the EET coupling and rate constant. We show that several architectures allow us to increase the EET rate by one order of magnitude compared to the original compound

Straightforward metal-free synthesis of an azacalix[6]arene forming a host–guest complex with fullerene C 60

International audienceElectronic 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

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

International audienceA 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 pi-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 alpha-positions of the pyrrole units through vinyl linkers, making these chromophores promising candidates for bioluminescence applications

Calculations of n →π* Transition Energies: Comparisons Between TD-DFT, ADC, CC, CASPT2, and BSE/ GW Descriptions

International audienceUsing a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), CASPT2, time-dependent density functional theory (TD-DFT), and BSE/evGW, the two latter combined with different exchange-correlation functionals, we investigate the lowest singlet transition in 23 n→π* compounds based on the nitroso, thiocarbonyl, carbonyl, and diazo chromophores. First, for 16 small derivatives we compare the transition energies provided by the different wave function approaches to define theoretical best estimates. For this set, it surprisingly turned out that ADC(2) offers a better match with CC3 than ADC(3). Next, we use 10 functionals belonging to the "LYP" and "M06" families and compare the TD-DFT and the BSE/evGW descriptions. The BSE/evGW results are less sensitive than their TD-DFT counterparts to the selected functional, especially in the M06 series. Nevertheless, BSE/evGW delivers larger errors than TD-CAM-B3LYP, which provides extremely accurate results in the present case, especially when the Tamm−Dancoff approximation is applied. In addition, we show that, among the different starting points for BSE/evGW calculations, M06-2X eigenstates stand as the most appropriate. Finally, we confirm that the trends observed on the small compounds pertain in larger molecules. ■ INTRODUCTION Like their ground-state (GS) counterparts, the theoretical methods that can be applied to model electronically excited-states (ES) can be roughly divided into two categories: single-reference and multireference approaches. 1 If the latter methods can accurately account for static correlation effects, the former theories have the indisputable advantage of allowing more black-box applications. Indeed, in multireference schemes, such as in the Complete Active Space with Second-order Perturbation Theory (CASPT2), 2 the selection of a chemically suitable active space and the follow-up of the calculations remain very consuming in terms of workforce. While single-determinant theories are obviously unsuited for intrinsically multireference cases, for example, conical intersections, they are more straightforward and are still used in the vast majority of ES applications devoted to the modeling of absorption, fluorescence, and phosphorescence spectra. Up to now, theoretical chemists had the choice between two families of single-reference approaches to treat ES. On the one hand, one finds Time-Dependent Density Functional Theory (TD-DFT), 3 an extension of DFT to ES that enjoys several advantages, among which, computational efficiency thanks to both a formal N () 4 scaling with system size and the implementations of analytical first (gradient) and second (Hessian) derivatives. 4,5 However, one of the most important limitations of TD-DFT is the dependency of the ES energies on the chosen exchange-correlation functional (XCF), a dependency that is generally much stronger than for GS properties, though it depends on the nature of the ES considered, 6 at least when the popular adiabatic formulation of TD-DFT is used. 7 I

Mixed N-Aryl/Alkyl Substitution Favours an Unusual Tautomer of Near-Infrared Absorbing Azacalixphyrins

International audienceAzacalixphyrins are bis-zwitterionic aromatic macrocycles that feature absorption properties in the near-infrared range. Their N-substitution is an efficient strategy for tuning the absorption maxima by stabilizing different tautomeric forms depending on the nature of the substituent (alkyl or aryl give 1-5 or 2-6 tautomers, respectively). This work depicts the synthesis of a new azacalixphyrin presenting both aryl and alkyl substituents. The joint experimental and theoretical study supports that the substitution pattern can be manipulated to counterbalance the repulsion of the two peripheral cationic charges to favour an unusual 5-7 tautomer

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

International audienceA 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 to control the canonical vs zwitterionic equilibrium through the tuning of the 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 vapochromic material. This latter experiment shows the first case of intramolecular solid-state proton transfer occurring in polar environment

Azacalixquinarenes: From Canonical to (Poly-)Zwitterionic Macrocycles

International audienceAzacalixquinarenes, a new family of macrocycles constituted of diaminobenzoquinone diimine units linked by dinitrobenzene rings are synthesized by selected oxidation of the parent azacalixarenes. Crystallographic analyses of two compounds demonstrated the presence of (uncharged) canoni-cal and zwitterionic quinones within a single structure. The electron-withdrawing nature of the dinitrobenzene moieties can trigger the intramolecular H-transfer that generates zwitterionic-ground state quinones. The nature of the N-substituents and the polarity of the solvent have a crucial impact on the equilibrium between the canonical and zwitterionic forms that present distinct optical and electrochemical properties. Thus, within [4]-and [6]-membered macrocycles, poly-zwitterionic structures can be reached, as demonstrated experimentally and theoretically using first-principle approaches

Synthesis and Characterization of Ruffled Phosphorus meso -Ester Corroles

International audienceThe strong electron-withdrawing character of 5,15-meso-ester groups was demonstrated through the study of four fluorescent hexacoordinate phosphorus(V) meso-substituted corroles, which were characterized by various techniques including single-crystal X-ray diffraction and first-principles calculations. The nature of the remaining meso substituent tunes the physicochemical properties of these phosphorus complexes only slightly but unexpectedly plays a key role in the ruffling of the macrocycle