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Multifunctional stimuli-responsive fluorophores showing bright environment-sensitive emissions have fueled intense research due to their innovative applications in the fields of biotechnologies, optoelectronics, and materials. A strong structural diversity is observed among molecular materials, which has been enriched over the years with a growing responsiveness to stimuli. Boron dipyrromethene (BODIPY) dyes have long been the flagship of emissive boron complexes due to their outstanding properties until a decade ago when analogues based on N^O, N^N, or N^C π-conjugated chelates emerged. The finality of developing borate dyes was to compensate for BODIPYs’ lack of solid-state fluorescence and small Stokes shifts while keeping their excellent optical properties in solution. Among them, the borate complexes based on a salicylaldimine ligand, called by the acronym boranils appear as the most promising, owing to their facile synthesis and dual-state emission properties. Boranil dyes have proven to be good alternatives to BODIPY dyes and have been applied in applications such as bioimaging, bioconjugation, and detection of biosubstrates. Meanwhile, ab initio calculations have rationalized experimental results and provided insightful feedback for future designs. This review article aims at providing a concise yet representative overview of the chemistry around the boranil core with the subsequent applications.

Using the density functional theory (DFT) formalism, we have investigated the properties of some arylsulphonyl indazole derivatives that we studied previously for their biological activity and susceptibility to interactions of azoles. This study includes the following physicochemical properties of these derivatives: electronegativity and polarisability (Mulliken charges, adjusted charge partitioning, and iterative-adjusted charge partitioning approaches); free energy of solvation (solvation model based on density model and M062X functional); highest occupied molecular orbital (HOMO)–lowest occupied molecular orbital (LUMO) gap together with the corresponding condensed Fukui functions, time-dependent DFT along with the UV spectra simulations using B3LYP, CAM-B3LYP, MPW1PW91, and WB97XD functionals, as well as linear response polarisable continuum model; and estimation of global chemical reactivity descriptors, particularly the chemical hardness factor. The charges on pyrrolic and pyridinic nitrogen (the latter one in the quinolone ring of compound 8, as well as condensed Fukui functions) reveal a significant role of these atoms in potential interactions of azole ligand–protein binding pocket. The lowest negative value of free energy of solvation can be attributed to carbazole 6, whereas pyrazole 7 has the least negative value of this energy. Moreover, the HOMO–LUMO gap and chemical hardness show that carbazole 6 and indole 5 exist as soft molecules, while fused pyrazole 7 has hard character.

International audience; Mono- and di-anchoring γ-pyranylidene-based organic dyes featuring D–π–A and D–(π–A)2 architectures have been engineered as sensitizers for applications in Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical and photovoltaic properties were further investigated. TD-DFT calculations were performed to rationalize the trends observed in the optical and electrochemical properties of the dyes. The investigation of the photovoltaic performances of this series of new dyes provided structure–property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer, the nature of the substituents on the pyranylidene electron donor moiety and the number of anchoring groups. Dye-Sensitized Solar Cells based on mono-anchoring dyes were more efficient than the corresponding cells based on di-anchoring analogues due to high dye loading. The highest Power Conversion Efficiency of 5.23% was achieved with the mono-anchoring 17a dye containing t-butyl substituent groups on the pyranylidene fragment and with one thienyl π-conjugated spacer.

Three new copper coordination compounds derived from 2,2-bis(hydroxymethyl)propionic acid (dmpa) and hexamethylenetetramine (hmta) were obtained and their crystal structures were determined. The stoichiometry of the reagents applied in the syntheses reflects the metal to ligand molar ratio in the formed solid products. Due to the multiple coordination modes of the used ligands, wide structural diversity was achieved among synthesized compounds, i.e., mononuclear [Cu(dmp)2(hmta)2(H2O)] (1), dinuclear [Cu2(dmp)4(hmta)2] (2), and 1D coordination polymer [Cu2(dmp)4(hmta)]n (3). Their supramolecular structures are governed by O—H•••O and O—H•••N hydrogen bonds. The compounds were characterized in terms of absorption (UV-Vis and IR) and thermal properties. The relationships between structural features and properties were discussed in detail. Owing to discrepancies in the coordination mode of a dmp ligand, bidentate chelating in 1, and bidentate bridging in 2 and 3, there is a noticeable change in the position of the bands corresponding to the stretching vibrations of the carboxylate group in the IR spectra. The differences in the structures of the compounds are also reflected in the nature and position of the UV-Vis absorption maxima, which are located at lower wavelengths for 1.

International audience; Detailed theoretical studies of Ni(II) complexes in a distorted square planar form and containing dithio and (P,P) chelating ligands were performed. These Ni(II) complexes are investigated for their use in dye-sensitized solar cells (DSSC). Structures and UV-Vis spectra are calculated at density functional theory (DFT) and time-dependent density functional theory (TD-DFT) theories using B3LYP and CAM-B3LYP functionals and 6-31G(d,p) and 6-31G+(d) basis set. Geometry optimizations result in excellent agreement with the experimental results. Moreover, the analysis of the frontier molecular orbitals (FMOs) allowed a detailed assignment and a clear analysis of the electronic transitions. The TD-DFT calculations reproduce the main spectroscopic properties observed and substituent effects. The results reveal that all absorption spectra are characterized by mixed character mainly dominated by metal to ligand and ligand to ligand charge transfer (MLCT and LLCT). We unveil how the substituent variations affect the DSSCs features of the complexes.; Nous avons mené des études théoriques détaillées sur des complexes de Ni(II) de structure plan carré déformé portant des ligands chélatants dithio et bis-phosphino. Ces études nous ont permis d’évaluer la possibilité d’utiliser ces complexes de Ni(II) dans des cellules solaires à pigment photosensible (DSSC). Nous avons modélisé la structure et calculé les spectres UV–vis de ces complexes selon la théorie de la fonctionnelle de la densité (DFT) et la DFT dépendante du temps (TD-DFT) en utilisant les fonctionnelles B3LYP et CAM-B3LYP avec les bases 6-31G(d,p) et 6-31G+(d). Les résultats des optimisations géométriques montrent une excellente concordance avec les résultats expérimentaux. De plus, l’analyse des orbitales moléculaires frontières (OMF) a permis de comprendre clairement et d’assigner en détail les transitions électroniques. Les calculs TD-DFT reproduisent les principales propriétés spectroscopiques observées et les effets des substituants. Selon nos résultats, tous les spectres d’absorption de ces complexes révèlent un caractère mixte dominé principalement par les transferts de charge métal vers ligand et ligand vers ligand. Nous présentons la façon dont les variations des substituants influent sur les propriétés des cellules solaires à pigment photosensible composées de ces complexes

The imino tautomers of isocytosine were objects of investigation at the TD-DFT level of theory - TD BLYP/6-311++G(d,p). We studied the mechanisms of the H1-N detachment in these tautomers through excited-state reaction paths. It was proposed that these transformations occur through the 1πσ* excited-state reaction paths of the imino tautomers. The mechanisms involve dissociations of the N1–H bonds in the tautomers and lead to crossings between the reaction paths of 1πσ* and S0 electronic states. One can suppose that such processes would facilitate the tautomerizations of the imino tautomers if further mechanisms have been found. This work is licensed under a Creative Commons Attribution 4.0 International License.

International audience; In this paper, we report the synthesis of new unsymmetrical azines Schiff bases. These compounds were prepared by condensation of hydrazine with different aldehydes and ketones to give (E) -2-hydroxynaphthalene-1-carbaldehyde [(1E) -2-thienylmethylene] hydrazone compound (I) and (Z) - 2 - [(E) -1- (2-hydroxyphenyl) ethylidenehydrazin-1-ylidene] -1,2-diphenylethanone compound (II). The method adopted consists in reacting the two different carbonyl compounds simultaneously in one step in a stepwise manner reported which is practical and cost-effective. The reaction with a minor modification in operating conditions proceeded efficiently and with excellent performance. The structure of each of the two compounds (I) and (II) was determined by the X-ray diffraction technique performed on single crystals. The asymmetric unity of the two molecules consists of one asymmetry-independent molecule. In addition, hydrogen bonds CH … π are observed in the compound (II). We then present a detailed DFT study based on B3LYP/6-31G (d, p) geometric structures of compounds (I); (II) and another compound (III) also another asymmetric azine (Z) -2 - [(E) -2-benzylidenehydrazine-1-ylidene] -1,2-diphenylethanone whose crystal structure is reported. The fundamental vibration wave numbers are calculated and a good agreement between the observed and calculated wave numbers is obtained. The study was extended to the HOMO-LUMO analysis to calculate the energy gap. The calculated HOMO and LUMO energy reveals that the charge is transferred into the molecule.

Thienoguanosine (th G) is an isomorphic analogue of guanosine with promising potentialities as fluorescent DNA label. As a free probe in protic solvents, th G exists in two tautomeric forms, identified as the H1, being the only one observed in nonprotic solvents, and H3 keto-amino tautomers. We herein investigate the photophysics of th G in solvents of different polarity, from water to dioxane, by combining time-resolved fluorescence with PCM/TD-DFT and CASSCF calculations. Fluorescence lifetimes of 14.5-20.5 and 7-13 ns were observed for the H1 and H3 tautomers, respectively, in the tested solvents. In methanol and ethanol, an additional fluorescent decay lifetime (≈3 ns) at the blue emission side (λ≈430 nm) as well as a 0.5 ns component with negative amplitude at the red edge of the spectrum, typical of an excited-state reaction, were observed. Our computational analysis explains the solvent effects observed on the tautomeric equilibrium. The main radiative and nonradiative deactivation routes have been mapped by PCM/TD-DFT calculations in solution and CASSCF in the gas phase. The most easily accessible conical intersection, involving an out-of plane motion of the sulfur atom in the five-membered ring of th G, is separated by a sizeable energy barrier (≥0.4 eV) from the minimum of the spectroscopic state, which explains the large experimental fluorescence quantum yield.

In this paper, we report the synthesis, structural characterization, and solvatochromic properties of a N-linked p-pyridiniumcalix[4]arenediol derivative 1. In the solid state, 1 forms a dimeric assembly stabilized by a network of weak H-bonding interactions involving acetonitrile solvent molecules. In solution, 1 shows a peculiar negative solvatochromism which was rationalized with the aid of TD-DFT calculations. The species responsible for this phenomenon is the monodeprotonated betainic form of 1 which is easily formed at pH close to neutrality.

Efficient monosubstitution of the non-iodinated, mono-iodinated and di-iodinated m-carborane cluster at one Ccluster has led to the preparation of three single organic molecule-carborane dyads (4–6), which exhibited exceptional fluorescence properties with quantum yield values of 100% in solution, for all of them, with maxima around 415 nm, which correspond to the locally excited state (LE) emission. These results suggest that simply linking the m-carborane fragment to one anthracene unit through a CH2 spacer produces a significant enhancement of the fluorescence in the final fluorophore, probably due to the free rotation of the anthracene linked to the Ccluster. Besides, the presence of one or two iodine atoms linked to boron atoms does not cause any influence on the photophysical properties of the dyads, as it is confirmed by TD-DFT calculations. Notably, the three conjugates show good fluorescence efficiency in the aggregate state with quantum yields in the range of 19–23%, which could be ascribed to the presence of CH2, particularly for 4, and the iodine atoms in 5 and 6, which prevent π–π stacking. All these results indicate that our dyads are extremely good emitters in solution while maintaining the emission properties in the aggregate state. Crystal packing, fingerprint plot analysis, and TD-DFT calculations for the three compounds support these results. Confocal microscopy studies show that 6 is the best-internalized compound by HeLa cells via endocytosis, although 4 and 5 also presented a high fluorescence intensity emission. Moreover, due to the blue emission, this compound is an excellent candidate to be applied as a fluorescent dye in bioimaging studies., The work was supported by the Spanish Ministerio de Economía y Competitividad, MINECO (CTQ2016-75150-R, MAT2017-86357-C3-3-R and “Severo Ochoa” Program for Centers of Excellence in R&D SEV-2015-0496) and Generalitat de Catalunya (2017/SGR/1720, 2017/SGR/503). Z. K. is grateful for the general support of the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement MSCA-IF-2016-751587. D. Ch.-L. acknowledges funding from the Intramural CSIC (201730I019) project. Theoretical calculations have been achieved using computers from the Supercomputing Centre of Catalonia (CESCA). The authors would like to thank the staff at the Servei de Microscòpia de la Universitat Autònoma de Barcelona., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

Synthesis of a new (E)-N1-((9-ethyl-9H-carbazol-3-yl)methylene)-5-nitrobenzene-1,2-diamine as a fluorescent chemosensor for selective detection of Fe3+ ion over a number of other metal ions is described. The method for the synthesis of the carbazole Schiff base was based on the condensation of carbazole-3-carbaldehyde with 4-nitro-o-phenyldiamine in dimethylformamide in a moderate yield. The structure of the final compound was characterized by H-1 NMR, (13) C NMR, IR, mass spectrometry, and single crystal X-ray diffraction. The final compound exhibited exceptional selective and sensitive turn-on fluorescence response to the Fe3+ cation. The fluorescent intensity of the final compound was increased 20-fold and the stoichiometry ratio of the final compound to Fe3+ was 1:1. The association constant and detection limit for Fe3+ ion were predicted from fluorescence titrations as (1.36 +/- 0.09).10(4) M-1 and 1.0 to 6.0 mu M, respectively. The photophysical behavior of the compound was further explored by DFT methods. The predicted UV-Vis spectrum by TDDFT calculations was compared to the observed absorption spectrum of the targeted compound. TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [113Z159] We thank the Research Fund of TUBITAK for the financial support given to the research project (project number: 113Z159) and allowing us to use their computer clusters and software packages for calculations. AK gratefully acknowledges Ricardo B Metz from the University of Massachusetts, for allowing him to use their computer clusters and software packages for calculations.

Hybrid gold nanoparticles covalently coated with 5,10,15-p-(ω-methoxy polyethyleneoxyphenyl)-20-p-(hydroxyphenyl) porphyrin molecules, having about 16 repetitive units in each of its poly(oxyethylene) branches, were synthesized and characterized by UV–vis, fluorescence, dynamic light scattering (DLS), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) measurements. Their [H3O+] optical sensing behavior was also studied and compared to that of the similar water-soluble star polymer 5,10,15,20-tetrakis p-[ω-methoxypoly(ethyleneoxy)]phenylporphyrin. Changing the pH of a solution, the UV–vis spectra of the PEGylate porphyrin gold nanoparticles conjugates showed the gradual disappearance of the Soret band at 424 nm and the progressive increase of a new band at 451 nm. Upon acidic titration, also the fluorescence spectra showed a gradual disappearing of the fluorescence at 654 nm. Moreover, an unusual B-Band red-shift and a decreasing of porphyrin core basicity were observed for this porphyrin bonded to the gold nanoparticle surfaces. To rationalize these phenomena an in silico TD-DFT calculation study was then conducted. For its properties, this new system: can be used in both aqueous and organic media; by a simple treatment of the solution at 80 °C under N2 gas stream the starting Soret signals can be recovered; the nanoparticles can be eventually removed from the solution by centrifugation.

The synthesis and characterization of different ether and ester derivatives of 8-hydroxyquinoline have been made. UV-visible and fluorescence spectra of these compounds have revealed spectral dependence on both solvent and O-substituent. The fluorescence intensity of ether derivatives revealed higher intensity for 8-octyloxyquinoline compared with 8-methoxyquinoline, whereas those of ester derivatives had less fluorescence than 8-hydroxyquinoline. Theoretical calculations based on Time-dependent density functional theory (TD-DFT) were carried out for the quinolin-8-yl benzoate (8-OateQ) compound to understand the effect of O-substituent on the electronic absorption of 8-hydroxyquinaline (8-HQ). The calculations revealed comparable results with those obtained from the experimental data. Optimized geometrical structure was calculated with DFT at B3LYP/6-311++G** level of theory. The results indicated that 8-OateQ is not a coplanar structure. The absorption spectra of the compound were computed in gas-phase and solvent using B3LYP and CAM-B3LYP methods with 6-311++G ** basis set. The agreement between calculated and experimental wavelengths was very good at CAM-B3LYP/6-311++G** level of theory.

A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor-π-Acceptor(+)) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the time resolved area normalised emission spectra in particular, revealed a peculiar multiple emissive behaviour and allowed the distinct emitting states to be remarkably distinguished from solvation dynamics, occurring in water in a similar timescale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated with specific local emissive minima in the potential energy surface of S1 on the ground of quantum-mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state is identified to be responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, with both the TICT and the PICT generated from LE by progressive torsion around the quasi-single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non-equilibrated Excited Rotamers (NEER) principle.

Distorted square pyramidal complexes [Cu(L1)(H2O)]·ClO4 (1), [Cu(L2)(H2O)]·ClO4 (2) and [Cu(L3)(H2O)]·ClO4 (3) (HL1 = o-{[2-(2-aminoethylamino)ethylimino]methyl}phenol; HL2 = 2-{[2-(2-aminoethylamino)ethylimino]methyl}-6-methoxyphenol; HL3 = o-{1-[2-(2-aminoethylamino)ethylimino]ethyl}phenol) have been synthesized, and characterized by X-ray crystallography and spectroscopic analysis. All the complexes exhibit fluorescence at room temperature [λex = 267 nm, λem = 312, 329 and 357 nm, φ = 0.52 for 1; λex = 272 nm, λem = 312, 329 and 355 nm, φ = 0.46 for 2; λex = 265 nm, λem = 312, 356 and 377 nm, φ = 0.33 for 3]. The electronic structure and photophysical properties of the ligands and complexes were calculated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods using the B3LYP, B3PW91 and MPW1PW91 functionals, with 6-31G (d-p) and LanL2DZ basis sets. The results of TD-DFT calculations are functional-dependent and among the functionals, B3LYP was able to best reproduce the experimental results. Catecholase activity of 1–3 has been investigated using 3,5-di-tert butyl catechol (3,5-DTBC) as the model substrate and found that complexes are active for catalyzing the aerobic oxidation of 3,5-DTBC to 3,5-di-tert butyl benzoquinone (3,5-DTBQ). The compound with more distorted square pyramidal geometry shows a higher rate of catalytic activity. All the complexes have been tested for their anticancer activities in human breast (MCF7) cancer cell lines. Complexes show dose dependent suppression of cell viability with IC50 values 30, 68 and >100 μM for 1, 2 and 3, respectively. Anticancer activities of 1–3 and cisplatin were compared, and found that 1–3 were relatively less active than cisplatin.

In this article, we describe the static gas-phase pyrolysis, microwave-induced pyrolysis, and photolysis reactions of trifluoromethyl sulfonyl dihydropyridines. The goal of this work was to find a methodology that allows obtaining of substituted pyridines-which are known to be difficult to synthesize-to be reused in a new substitution reaction. We demonstrated that it is possible to achieve the rearomatization process by the elimination of the trifluoromethyl sulfonyl moiety through the 3 processes, with the static pyrolysis being the best method to obtain the substituted pyridines. In addition, we propose the 1,4-elimination (CF3SO2 + H) as the first step, since it is the less energetic process, as has also been corroborated by calculations. A competitive reaction (CO2 extrusion) also occurs, yielding undesired products. Copyright Fil: Firpo, Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Cooke, María Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Peláez, Walter José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Chans, Guillermo Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Anáhuac; México Fil: Argüello, Gustavo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Gómez, Elizabeth. Universidad Nacional Autónoma de México; México Fil: Alvarez Toledano, Cecilio. Universidad Nacional Autónoma de México; México

Selenium has been increasingly recognized as an important element in biological systems, which participates in numerous biochemical processes in organisms, notably in enzyme reactions. Selenium can substitute sulfur of cysteine and methionine to form their selenium analogues, selenocysteine (Sec) and selenomethionine (SeM). The nature of amino acid pockets in proteins is dependent on their composition and thus different non-covalent forces determine the interactions between selenium of Sec or SeM and other functional groups, resulting in specific biophysical behavior. The discrimination of selenium toward sulfur has been reported. In order to elucidate the difference between the nature of S-pi and Se-pi interactions, we performed extensive DFT calculations of dispersive and electrostatic contributions of Se-pi interactions in substituted benzenes/hydrogen selenide (H2Se) complexes. The results are compared with our earlier reported S-pi calculations, as well as with available experimental data. Our results show a larger contribution of dispersive interactions in Se-pi systems than in S-pi ones, which mainly originate from the attraction between Se and substituent groups. We found that selenium exhibits a strong interaction with aromatic systems and may thus play a significant role in stabilizing protein folds and protein-inhibitor complexes. Our findings can also provide molecular insights for understanding enzymatic specificity discrimination between single selenium versus a sulfur atom, notwithstanding their very similar chemical properties.

International audience; In this paper, we present a novel concept for "smarter" photolabile organic compounds combining not one but two caged functions. As proof of principle, this diarylethene-based compound possesses two inhibited chemical groups (OMe and OAc) and its efficient release in different solvents is reported. In low- to medium-polarity media, both MeOH and AcOH are released, with a slight preferential uncaging of AcOH except in 1,4-dioxane, where MeOH is preferentially released. In contrast, DMSO or DMF render AcOH release strongly dominating. DFT calculations of the corresponding photoreactive conformations not only afford strong support to the observed release of MeOH and AcOH but also qualitatively explain the preferential release of acid in terms of dispersive noncovalent interactions. Finally, mechanistic aspects are discussed on the bases of the spectroscopic observations and of the TD-DFT calculations.

A series of dithienophenazines with different lengths of the oligomeric thiophene units (quaterthiophenes and sexithiophenes) was synthesized. The thiophene and phenazine units act as electron donors and acceptors, respectively, resulting in characteristic absorption spectra. The optical spectra were calculated using time-dependent density functional theory at the B3LYP/TZVP level and verify the experimental data. Adsorption of the dithienophenazines on highly ordered pyrolytic graphite (HOPG) was investigated by scanning tunneling microscopy, showing that one of the compounds forms highly organized self-assembled monolayers.

International audience; The reaction between the 4,5-bis(2-pyridyl-N-oxidemethylthio)-4′,5′-dicarboxylic acid-tetrathiafulvalene-, dimethyl ester ligand (L) and the metallo-precursors Ln(hfac)3·2H2O leads to the formation of two dinuclear complexes of formula [Ln2(hfac)6(L)]·(CH2Cl2)·(C6H14)0.5 (LnIII = DyIII (1) and YbIII (2)). The X-ray structure reveals a quite regular square anti-prism symmetry for the coordination sphere of the lanthanide ion. UV-visible absorption properties have been experimentally measured and rationalized by TD-DFT calculations. The functionalization of the tetrathiafulvalene (TTF) core by two methyl ester moieties induces the appearance of an additional absorption band in the lowest-energy region of the spectrum. The latter has been identified as a HOMO (Highest Occupied Molecular Orbital)→LUMO (Lowest Unoccupied Molecular Orbital) Intra-Ligand Charge Transfer (ILCT) transition in which the HOMO and LUMO are centred on the TTF and methyl ester groups, respectively. Irradiation at 22,222 cm−1 of this ILCT band induces an efficient sensitization of the YbIII-centred emission that can be correlated to the magnetic properties.

A new approach to benzo[f]quinoline derivatives has been found by an effective formal [4 + 2] photocycloaddition process from novel aryl-substituted o-vinylstyryl-2-oxazoles. All of the o-vinylstyryl-2-oxazoles were synthesized by a multicomponent Wittig reaction from the diphosphonium salt of α,α'-o-xylene dibromide, formaldehyde, and 5-tolyl-, 4-phenyl-5-methyl-, and 4,5-diphenyloxazole-2-carbaldehydes. TD-DFT calculations revealed that the intramolecular photocyclization in 2-(2-vinylstyryl)oxazoles to form benzo[f]quinoline derivatives proceeds on the S1 PES via a stepwise pathway, namely by 10π followed by 6π ring closure. On that path the existence of an S0/S1 conical intersection was indicated. The reactivity of the photocyclization steps depends on the substitution pattern at positions 4 and 5 of the oxazole ring, where the aryl group in position 5 deactivates the reaction.

The chiroptical properties of enantiomerically pure bicyclo[3.3.1]nona-2,6-diene-2,6-dicarbonitrile and related acids were studied by circular dichroism spectroscopy and theoretical computations. A consideration of the molecular structure of the synthesized difunctional compounds revealed that chromophores are predisposed to transannular through-space interaction due to a favourable conformation of the bicyclic skeleton and a rather small interchromophoric distance. Evidence for non-exciton-type coupling between the two acrylonitrile and acrylate moieties in 3 and 4, respectively, was obtained by chiroptical spectroscopy and DFT calculations.

Four novel 6-aminocoumarin-naphthoquinone conjugates were synthesized and their photophysical and electrochemical properties, investigated. 2-Chloro-3-(2-oxo-2H-chromen-6-ylamino)-1,4-naphthoquinone 1 did not present appreciable fluorescence in solution in comparison with 6-aminocoumarin, 6-AC. In order to understand the reasons for the fluorescence quenching in this compound, two strategies were attempted. Firstly, compound 1 was N-methylated to remove the intramolecular N-H...O=C electrostatic interaction that maintained the two units fixed, but the emission properties of the product 2 were not significantly different from those of 1. Time-dependent density functional theory (TD-DFT) calculations of compounds 1 and 2 indicate that the fluorescence quenching is related to the electron acceptor character of the naphthoquinone ring. The second strategy, therefore, involved the substitution of the chlorine atom in position 2 of the naphthoquinone nucleus for different electron donor groups (compounds 3-5), but again the emission properties did not change significantly. To explain these experimental findings, TD-DFT calculations of the ground (S0) and excited (S1) states of all molecules in solution were carried out. The results suggest that the energy states in these conjugates are such that the fluorescent group (6-AC) donates electrons to the naphthoquinone LUMO resulting in an oxidative photoinduced electron transfer (oxidative-PET). Quatro novos conjugados do tipo 6-aminocumarina-naftoquinona foram sintetizados e suas propriedades fotofísicas e eletroquímicas, investigadas. O composto 2-cloro-3-(2-oxo-2H-cromen-6-ilamino)-1,4-naftoquinona 1 não apresentou fluorescência apreciável, em comparação com a 6-aminocumarina, 6-AC. Visando entender as razões da extinção da fluorescência neste composto, duas estratégias foram imaginadas. Primeiramente, o composto 1 foi metilado no nitrogênio para remover a interação eletrostática intramolecular N-H...O=C que mantém as duas unidades fixas. Entretanto, as propriedades de emissão do produto 2 não se mostraram significantemente diferentes das do precursor 1. Como os cálculos usando a teoria do funcional da densidade dependente do tempo (TD-DFT) dos compostos 1 e 2 indicaram que a supressão da fluorescência relaciona-se ao caráter aceptor no anel naftoquinônico, a segunda estratégia envolveu a substituição do átomo de cloro na posição 2 do núcleo naftoquinônico por diferentes grupos doadores de elétrons (compostos 3-5). Novamente não houve mudanças apreciáveis nas propriedades de emissão. Para explicar estes resultados foram feitos cálculos TD-DFT dos estados fundamental (S0) e excitado (S1) de todas as moléculas em solução, os quais indicaram que o grupo fluorescente (6-AC) doa elétrons para o LUMO da naftoquinona, resultando em uma transferência de elétron fotoinduzida oxidativa (oxidative-PET).

Four novel gem -silanediol-containing organic dyes featuring a highly conjugated backbone have been synthesized in order to investigate their potential as active materials for photovoltaics. After spectroscopic characterization, the compounds showing the best light harvesting and electrochemical properties were applied as sensitizers in dye-sensitized solar cells (DSSCs). Interestingly, photovoltaic cells built using the new silanediol dyes showed low power conversion efficiencies ( η ), comparable to those obtained with silicon-based sensitizers having simple azobenzene moieties as the light-harvesting units. Such values are mostly due to unsatisfactory photocurrent densities; a computational study suggested that the latter can be justified considering the insufficient degree of charge transfer taking place during photoexcitation of the silicon-containing sensitizers, which is likely to make electron injection into the TiO 2 layer less efficient.

The complexes of the general formulae [Ru(terpy)(dcbpy)X](q) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine; X = Cl(-), 1; NO(+), 2: No(2)(-), 3: q = 1+, 3+ and 1-, respectively) have been synthesized and characterized. The DNA binding properties of structurally similar complexes [Ru(terpy)(dcbpy)NO(2)](-), 3, [Ru(terpy)(4-CO(2)-4'-Mebpy)NO(2)], 4, and [Ru(terpy)(bpy)NO(2)](+), 5, were studied, and their DNA affinities (K(b)) were calculated as 6 +/- 0.3 x 10(4) M(-1), 8 +/- 1.1 x 10(4) M(-1) and 9.7 +/- 0.02. 10(6) M(-1). The structural and spectroscopic properties of complexes 3-5 were investigated by DFT and TD DFT electronic structure calculations. The equilibrium geometries of complexes 3-5 in vacuum correspond to a distorted octahedral stereochemistry. The high-lying peaks of the absorption spectra of the complexes, ranging from 440 to 529 nm, are assigned to MLCT/LLCT transitions. These transitions are red-shifted upon adding carboxy substituents to the bipyridine ligand while the low-lying LLCT transitions, absorbing at 779 and 659 turn, are blue-shifted. Noteworthy is the excellent agreement of the TD DFT simulated absorption spectra in aqueous solution with the experimental ones. (C) 2008 Elsevier B.V. All rights reserved. Inorganic Chemistry Communications