Publications by authors named "Tangui Le Bahers"

27 Publications

  • Page 1 of 1

Tuning Excited-State Properties of [2.2]Paracyclophane-Based Antennas to Ensure Efficient Sensitization of Lanthanide Ions or Singlet Oxygen Generation.

Inorg Chem 2021 Nov 12;60(21):16194-16203. Epub 2021 Oct 12.

Univ Paris, Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, CNRS UMR 8601, 45 Rue des Saints Pères, 75006 Paris, France.

The multistep synthesis of original antennas incorporating substituted [2.2]paracyclophane (pCp) moieties in the π-conjugated skeleton is described. These antennas, functionalized with an electron donor alkoxy fragment () or with a fused coumarin derivative (), are incorporated in a triazacyclonane macrocyclic ligand or , respectively, for the design of Eu(III), Yb(III), and Gd(III) complexes. A combined photophysical/theoretical study reveals that presents a charge transfer character via through-space paracyclophane conjugation, whereas presents only local excited states centered on the coumarin-paracyclophane moiety, strongly favoring triplet state population via intersystem crossing. The resulting complexes Eu and Yb are fully emissive in red and near-infrared, respectively, whereas the Gd complex acts as a photosensitizer for the generation of singlet oxygen.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.inorgchem.1c01986DOI Listing
November 2021

Light-induced in situ chemical activation of a fluorescent probe for monitoring intracellular G-quadruplex structures.

Nanoscale 2021 Aug 4;13(32):13795-13808. Epub 2021 Aug 4.

Department of Medical Biochemistry and Biophysics, Umeå University, 90187 Umeå, Sweden.

Light-activated functional materials capable of remote control over duplex and G-quadruplex (G4) nucleic acids formation at the cellular level are still very rare. Herein, we report on the photoinduced macrocyclisation of a helicenoid quinoline derivative of binaphthol that selectively provides easy access to an unprecedented class of extended heteroaromatic structures with remarkable photophysical and DNA/RNA binding properties. Thus, while the native bisquinoline precursor shows no DNA binding activity, the new in situ photochemically generated probe features high association constants to DNA and RNA G4s. The latter inhibits DNA synthesis by selectively stabilizing G4 structures associated with oncogenic promoters and telomere repeat units. Finally, the light sensitive compound is capable of in cellulo photoconversion, localizes primarily in the G4-rich sites of cancer cells, competes with a well-known G4 binder and shows a clear nuclear co-localization with the quadruplex specific antibody BG4. This work provides a benchmark for the future design and development of a brand-new generation of light-activated target-selective G4-binders.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d1nr02855cDOI Listing
August 2021

2D MoOS/MoS van der Waals Assembly: A Tunable Heterojunction with Attractive Properties for Photocatalysis.

ACS Appl Mater Interfaces 2021 Aug 26;13(30):36465-36474. Epub 2021 Jul 26.

Univ Lyon, ENS de Lyon, CNRS, Université Claude Bernard Lyon 1, Laboratoire de Chimie UMR 5182, F-69342 Lyon, France.

Two-dimensional (2D) van der Waals (vdW) heterostructures currently have attracted much attention in widespread research fields where semiconductor materials are key. With the aim of gaining insights into photocatalytic materials, we use density functional theory (DFT) calculations within the HSE06 functional to analyze the evolution of optoelectronic properties and high-frequency dielectric constant profiles of various 2D MoOS/MoS heterostructures modified by chemical and physical approaches. Although the MoO/MoS heterostructure is a type III heterojunction associated with a metallic character, we found that exchanging the terminal oxo atoms of the MoOS single layer (SL) with sulfur enables shifting its CB position above the VB position of the MoS SL. This trend gives rise to a type II heterojunction where the band gap and charge transfer within the two layers are driven continuously by the S concentration in the MoOS SL. This fine-tuning leads to a versatile type II heterostructure proposed to provide a direct Z-scheme system valuable for photocatalytic water splitting.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c08200DOI Listing
August 2021

Exploring the Concept of Dimerization-Induced Intersystem Crossing: At the Origins of Spin-Orbit Coupling Selection Rules.

J Phys Chem B 2021 08 22;125(30):8572-8580. Epub 2021 Jul 22.

Univ Lyon, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, F-69342 Lyon, France.

Singlet-triplet interconversions (intersystem crossing, ISC) in organic molecules are at the basis of many important processes in cutting-edge photonic applications (organic light-emitting devices, photodynamic therapy, etc.). Selection rules for these transitions are mainly governed by the spin-orbit coupling (SOC) phenomenon. Although the SOC relies on complex relativistic phenomena, theoreticians have, with time, developed increasingly sophisticated and efficient approaches to gain access to a satisfactory evaluation of its magnitude. However, recent works have highlighted the remarkable and somehow unexpected efficiency of dimers of small conjugated molecules in terms of ISC quantum yields, whose origin has not been completely investigated. In this work, we bring a coupled experimental and theoretical analysis of the origin of the unusually large ISC efficiency on a series of such dimers that differ by their nature (covalent or supramolecular). We show that considering the dynamical nature of the SOC, and especially its dependence on angular orientations between the dimer subunits sometimes overlooked in the literature, it is necessary to rationalize some counterintuitive experimental observations. This combined experimental and theoretical work paves the way for new molecular engineering rules for SOC control.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpcb.1c05082DOI Listing
August 2021

Spin-orbital coupling and slow phonon effects enabled persistent photoluminescence in organic crystal under isomer doping.

Nat Commun 2021 Jun 9;12(1):3485. Epub 2021 Jun 9.

Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA.

When periodically packing the intramolecular donor-acceptor structures to form ferroelectric-like lattice identified by second harmonic generation, our CD49 molecular crystal shows long-wavelength persistent photoluminescence peaked at 542 nm with the lifetime of 0.43 s, in addition to the short-wavelength prompt photoluminescence peaked at 363 nm with the lifetime of 0.45 ns. Interestingly, the long-wavelength persistent photoluminescence demonstrates magnetic field effects, showing as crystalline intermolecular charge-transfer excitons with singlet spin characteristics formed within ferroelectric-like lattice based on internal minority/majority carrier-balancing mechanism activated by isomer doping effects towards increasing electron-hole pairing probability. Our photoinduced Raman spectroscopy reveals the unusual slow relaxation of photoexcited lattice vibrations, indicating slow phonon effects occurring in ferroelectric-like lattice. Here, we show that crystalline intermolecular charge-transfer excitons are interacted with ferroelectric-like lattice, leading to exciton-lattice coupling within periodically packed intramolecular donor-acceptor structures to evolve ultralong-lived crystalline light-emitting states through slow phonon effects in ferroelectric light-emitting organic crystal.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-021-23791-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8190285PMC
June 2021

Investigation of the K[Fe(CN)]-Mediated Mono- and Bis-Palladium-Catalyzed Cyanation of the Benzothioxanthene Core.

J Org Chem 2021 04 1;86(8):5901-5907. Epub 2021 Apr 1.

Université Angers, CNRS, MOLTECH-Anjou, SFR MATRIX, F-49000 Angers, France.

The pallado-catalyzed cyanation of benzothioxanthene imide () derivatives is explored herein. Once optimized on the monobromo , mild reaction conditions were successfully applied to the dibromo derivative affording two regioisomers that have been isolated and structurally solved. Additional hydrogen-deuterium exchange experiments were carried out to support a proposed mechanism involving the formation of a five-membered palladacycle intermediate in the bay area. As well as impacting the structural, photo physical and electrochemical properties of the core, nitrile moieties were successfully used as orthogonal protecting groups, thus opening doors to new design principles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.joc.1c00318DOI Listing
April 2021

What does graphitic carbon nitride really look like?

Phys Chem Chem Phys 2021 Feb;23(4):2853-2859

Université de Lyon, Université Claude Bernard Lyon 1, Ecole Normale Supérieure de Lyon, CNRS, 46 allée d'Italie, F-69007 Lyon Cedex, France.

Graphitic carbon nitrides (g-CNs) have become popular light absorbers in photocatalytic water splitting cells. Early theoretical work on these structures focused on fully polymerized g-C3N4. Experimentally, it is known that the typically employed melamine polycondensation does not go toward completion, yielding structures with ∼15 at% hydrogen. Here, we study the conformational stability of "melon", with the [C6N9H3]n structural formula using DFT. Referencing to a 2D melon sheet, B3LYP-dDsC and PBE-MBD computations revealed the same qualitative trend in stability of the 3D structures, with several of them within 5 kJ mol-1 per tecton. Fina's orthorhombic melon is the most stable of the studied conformers, with Lotsch' monoclinic melon taking an intermediate value. Invoking a simple Wannier-Mott-type approach, Fina's and Lotsch' structures exhibited the lowest optical gaps (2.8 eV), within the error margin of the experimental value (2.7 eV). All conformers yielded gaps below that of the monolayer's (3.2 eV), suggesting Jelley-type ("J") aggregation effects.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0cp06063aDOI Listing
February 2021

Two-Photon Absorbing AIEgens: Influence of Stereoconfiguration on Their Crystallinity and Spectroscopic Properties and Applications in Bioimaging.

ACS Appl Mater Interfaces 2020 Dec 20;12(49):55157-55168. Epub 2020 Nov 20.

Univ. Lyon, ENS Lyon, CNRS, Université Lyon 1, Laboratoire de Chimie, UMR 5182, 46 Allée d'Italie, 69364 Lyon, France.

This paper aims at designing chromophores with efficient aggregation-induced emission (AIE) properties for two-photon fluorescence microscopy (2PFM), which is one of the best-suited types of microscopy for the imaging of living organisms or thick biological tissues. Tetraphenylethylene (TPE) derivatives are common building blocks in the design of chromophores with efficient AIE properties. Therefore, in this study, extended TPE AIEgens specifically optimized for two-photon absorption (2PA) are synthesized and the resulting (/) isomers are separated using chromatography on chiral supports. Comparative characterization of the AIE properties is performed on the pure () and () isomers and the mixture, allowing us, in combination with powder X-ray diffraction and solid-state NMR, to document a profound impact of crystallinity on solid-state fluorescence properties. In particular, we show that stereopure AIEgens form aggregates of superior crystallinity, which in turn exhibit a higher fluorescence quantum yield compared to diastereoisomers mixtures. Preparation of stereopure organic nanoparticles affords very bright fluorescent contrast agents, which are then used for cellular and intravital two-photon microscopy on human breast cancer cells and on zebrafish embryos.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c15810DOI Listing
December 2020

σ-Conjugation and H-Bond-Directed Supramolecular Self-Assembly: Key Features for Efficient Long-Lived Room Temperature Phosphorescent Organic Molecular Crystals.

Angew Chem Int Ed Engl 2021 Feb 1;60(5):2446-2454. Epub 2020 Dec 1.

Building Blocks for FUture Electronics Laboratory, UMI 2002, CNRS-Sorbonne Université-Yonsei University, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, 03722, South Korea.

Long-lived room temperature phosphorescence from organic molecular crystals attracts great attention. Persistent luminescence depends on the electronic properties of the molecular components, mainly π-conjugated donor-acceptor (D-A) chromophores, and their molecular packing. Here, a strategy is developed by designing two isomeric molecular phosphors incorporating and combining a bridge for σ-conjugation between the D and A units and a structure-directing unit for H-bond-directed supramolecular self-assembly. Calculations highlight the critical role played by the two degrees of freedom of the σ-conjugated bridge on the chromophore optical properties. The molecular crystals exhibit RTP quantum yields up to 20 % and lifetimes up to 520 ms. The crystal structures of the efficient phosphorescent materials establish the existence of an unprecedented well-organization of the emitters into 2D rectangular columnar-like supramolecular structure stabilized by intermolecular H-bonding.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202011770DOI Listing
February 2021

Theoretical and experimental investigation on the intersystem crossing kinetics in benzothioxanthene imide luminophores, and their dependence on substituent effects.

Phys Chem Chem Phys 2020 Jun 20;22(22):12373-12381. Epub 2020 Apr 20.

Univ. Lyon, ENS Lyon, CNRS, Université Lyon 1, Laboratoire de Chimie, UMR 5182, 46 Allée d'Italie, 69364 Lyon, France.

In spite of their remarkable luminescence properties, benzothioxanthene imide (BTXI, an imide containing rylene chromophores) derivatives have been largely overlooked compared to their perylene bisimide and naphthalene bisimide counterparts. Thus, their detailed photophysics are much less understood. In this paper, we show how relatively simple structural modifications of the backbone of BTXIs can lead to impressive variations in their inter-system crossing kinetics. Thus, through rational engineering of their structure, it is possible to obtain a triplet formation quantum yield that reaches unity, making BTXI a promising class of compounds for triplet-based applications (photodynamic therapy, electroluminescence, etc.).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0cp01072cDOI Listing
June 2020

Two-sites are better than one: revisiting the OER mechanism on CoOOH by DFT with electrode polarization.

Phys Chem Chem Phys 2020 Apr;22(13):7031-7038

Univ Lyon, ENS de Lyon, CNRS, Université Lyon 1, Laboratoire de Chimie UMR 5182, Lyon, France.

We uncover the existence of several competitive mechanisms of water oxidation on the β-CoOOH (10-14) surface by going beyond the classical 4-step mechanism frequently used to study this reaction at the DFT level. Our results demonstrate the importance of two-site reactivity and of purely chemical steps with the associated activation energies. Taking the electrochemical potential explicitly into account leads to modifications of the reaction energy profiles finally leading to the proposition of a new family of mechanisms involving tetraoxidane intermediates. The two-site mechanisms revealed in this work are of key importance to rationalize and predict the impact of dopants in the design of future catalysts.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0cp00281jDOI Listing
April 2020

A "Multi-Heavy-Atom" Approach toward Biphotonic Photosensitizers with Improved Singlet-Oxygen Generation Properties.

Chemistry 2019 Jul 30;25(38):9026-9034. Epub 2019 May 30.

Laboratoire de Chimie de l'ENS de Lyon, Univ Lyon, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard Lyon 1, 69342, Lyon, France.

Two trispicolinate 1,4,7-triazacyclonane (TACN)-based ligands bearing three picolinate biphotonic antennae were synthetized and their Yb and Gd complexes isolated. One series differs from the other by the absence (L )/presence (L ) of bromine atoms on the antenna backbone, offering respectively improved optical and singlet-oxygen generation properties. Photophysical properties of the ligands, complexes and micellar Pluronic suspensions were investigated. Complexes exhibit high two-photon absorption cross-section combined either with NIR emission (Yb) or excellent O generation (Gd). The very large intersystem crossing efficiency induced by the combination of bromine atom and heavy rare-earth element was corroborated with theoretical calculations. The O generation properties of L Gd micellar suspension under two-photon activation leads to tumour cell death, suggesting the potential of such structures for theranostic applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/chem.201901047DOI Listing
July 2019

Ab initio assessment of BiRECuOS (RE = La, Gd, Y, Lu) solid solutions as a semiconductor for photochemical water splitting.

Phys Chem Chem Phys 2017 May;19(19):12321-12330

King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC) and Physical Sciences and Engineering Division (PSE), 4700 KAUST, Thuwal, 23955-6900, Saudi Arabia.

The investigation of the BiCuOCh (Ch = S, Se and Te) semiconductor family for thermoelectric or photovoltaic materials is a topic of increasing research interest. These materials can also be considered for photochemical water splitting if one representative having a bandgap, E, at around 2 eV can be developed. With this aim, we simulated the solid solutions BiRECuOS (RE = Y, La, Gd and Lu) from pure BiCuOS (E ∼ 1.1 eV) to pure RECuOS compositions (E ∼ 2.9 eV) by DFT calculations based on the HSE06 range-separated hybrid functional with the inclusion of spin-orbit coupling. Starting from the thermodynamic stability of the solid solution, several properties were computed for each system including bandgaps, dielectric constants, effective masses and exciton binding energies. We discussed the variation of these properties based on the relative organization of Bi and RE atoms in their common sublattice to offer a physical understanding of the influence of the RE doping of BiCuOS. Some compositions were found to give appropriate properties for water splitting applications. Furthermore, we found that at low RE fractions the transport properties of BiCuOS are improved that can find applications beyond water splitting.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c7cp01684kDOI Listing
May 2017

Modeling the Photochromism of S-Doped Sodalites Using DFT, TD-DFT, and SAC-CI Methods.

Inorg Chem 2017 Jan 15;56(1):414-423. Epub 2016 Dec 15.

Univ Lyon, ENS de Lyon, CNRS, Université Claude Bernard Lyon 1, Laboratoire de Chimie UMR 5182, F-69342 Lyon, France.

S-doped sodalite minerals of the NaAlSiO(Cl,S) formula, also known as hackmanites, are computationally investigated for the first time, in order to understand their photochromic properties. With combined periodic boundary conditions and embedded cluster-type approaches, this paper brings a theoretical overview of the photochromism mechanism, also called tenebrescence in geology. Time-dependent density functional theory (TD-DFT) calculations of sodalite systems containing electrons trapped in Cl vacancies showed an absorption spectrum and a simulated color in agreement with experiment. This modeling highlights the huge effect of the F center's environment such as the direct contribution of the β cage on the trapped electron and a strong vibronic coupling of the absorption spectrum. TD-DFT and post-Hartree-Fock (SAC-CI) calculations were also operated on S-containing systems in order to determine the exact mechanism of coloration and discoloration, supporting that the key step is a direct through-space charge transfer between the S ion and a Cl vacancy. The geometry modification induced by this charge transfer leads to a large electronic reorganization stabilizing the F center, thus explaining the high stability of the colored state of the mineral.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.inorgchem.6b02323DOI Listing
January 2017

Carbazole-Substituted Iridium Complex as a Solid State Emitter for Two-Photon Intravital Imaging.

Inorg Chem 2016 Oct 12;55(19):9586-9595. Epub 2016 Sep 12.

Laboratoire de Chimie, ENS de Lyon, CNRS UMR 5182, Université Claude Bernard, Université de Lyon , F69342 Lyon, France.

A tris-cyclometalated iridium complex that bears two ligands functionalized by peripheral carbazole groups combines an intense solid state emission and a significant two-photon absorption cross section in the near-infrared. After incorporation into a physiological micellar suspension, it can be used for the intravital two-photon fluorescence microscopy of cerebral vasculature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.inorgchem.6b01253DOI Listing
October 2016

Assembly of Ferrocene Molecules on Metal Surfaces Revisited.

J Phys Chem Lett 2015 Feb 16;6(3):395-400. Epub 2015 Jan 16.

†Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg, UMR CNRS 7504, 67034 Strasbourg, France.

Metallocene (MCp2) wires have recently attracted considerable interest in relation to molecular spintronics due to predictions concerning their half-metallic nature. This exciting prospect is however hampered by the little and often-contradictory knowledge we have concerning the metallocene self-assembly and interaction with a metal. Here, we elucidate these aspects by focusing on the adsorption of ferrocene on Cu(111) and Cu(100). Combining low-temperature scanning tunneling microscopy and density functional theory calculations, we demonstrate that the two-dimensional molecular arrangement consists of vertical- and horizontal-lying molecules. The noncovalent T-shaped interactions between Cp rings of vertical and horizontal molecules are essential for the stability of the physisorbed molecular layer. These results provide a fresh insight into ferrocene adsorption on surfaces and may serve as an archetypal reference for future work with this important variety of organometallic molecules.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jz5026118DOI Listing
February 2015

Electronic properties of PbX₃CH₃NH₃ (X = Cl, Br, I) compounds for photovoltaic and photocatalytic applications.

Phys Chem Chem Phys 2015 Jan 8;17(3):2199-209. Epub 2014 Dec 8.

Université de Lyon, Université Claude Bernard Lyon1, Centre National de Recherche Scientifique, ENS Lyon, 46 allée d'Italie, 69007 Lyon Cedex 07, France.

Since the discovery of their excellent performance as the light-absorbing semiconducting component in photovoltaic cells, the PbX3CH3NH3 (X = I, Br, Cl) perovskites have received renewed attention. The five polymorphs stable above 200 K - the tetragonal phases for X = I, Br, Cl and the cubic phases for X = I, Br - were studied using periodic DFT calculations involving hybrid functionals (PBE0 and HSE), employing Gaussian-type orbitals as well as plane waves and including relativistic effects (spin-orbit coupling). The influence of the halogen substitution and of the crystal phase on these properties is analysed by comparing the properties obtained in this study to the experimental ones and to the theoretical ones computed using other methods. We show that an accurate treatment of these systems requires the description of dispersion forces and spin-orbit coupling. The different time scales for the electronic and vibrational components of the polarizability inspire the hypothesis that several interfacial charge transfer mechanisms are encountered in the working principle of the photovoltaic devices involving these perovskite materials. The heavy elements in the structure (Pb, I) play a major role in the high polarizability and the low effective charge carrier masses and hence in the low exciton binding energies and the high charge mobility. This systematic work on the PbX3CH3NH3 family offers to theoreticians an overview of the landscape of quantum chemical methods to enable a reasonable choice of methodology for studying these systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c4cp04666hDOI Listing
January 2015

The nature of vertical excited states of dyes containing metals for DSSC applications: insights from TD-DFT and density based indexes.

Phys Chem Chem Phys 2014 Jul;16(28):14435-44

Université Claude Bernard Lyon 1, ENS Lyon, Centre Nationale de Recherche Scientifique (CNRS), 46 allée d'Italie, 69364 Lyon Cedex 07, France.

Transition metal complexes, typically Ru-based complexes, are the most efficient dyes used in dye-sensitized solar cells. The absorption spectra of these molecules generally involve numerous electronic transitions, which are not equivalent for the conversion of the light into electricity. In the present manuscript, an analysis of each electronic transition of selected inorganic complexes is performed based on the variation of the electronic density upon light absorption. To this end, a series of indices recently proposed in the literature is applied. The main conclusions of this work are twofold: from a methodological point of view, global hybrid functionals confirm their robustness for studying the electronic transitions of these compounds and from an application oriented point of view it is clear that the most intense transitions are not necessarily the most efficient ones for the light conversion.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c3cp55032jDOI Listing
July 2014

Modeling Dye-Sensitized Solar Cells: From Theory to Experiment.

J Phys Chem Lett 2013 Mar 18;4(6):1044-50. Epub 2013 Mar 18.

‡LECIME, Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, UMR 7575 CNRS, Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

Density functional theory (DFT) and time-dependent DFT are useful computational approaches frequently used in the dye-sensitized solar cell (DSSC) community in order to analyze experimental results and to clarify the elementary processes involved in the working principles of these devices. Indeed, despite these significant contributions, these methods can provide insights that go well beyond a purely descriptive aim, especially when suitable computational approaches and methodologies for interpreting and validating the computational outcomes are developed. In the present contribution, the possibility of using recently developed computational approaches to design and interpret the macroscopic behavior of DSSCs is exemplified by the study of the performances of three new TiO2-based DSSCs making use of organic dyes, all belonging to the expanded pyridinium family.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jz400046pDOI Listing
March 2013

First-principles modeling of dye-sensitized solar cells: challenges and perspectives.

Acc Chem Res 2012 Aug 12;45(8):1268-77. Epub 2012 Apr 12.

Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, UMR CNRS, Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech, France.

Since dye-sensitized solar cells (DSSCs) appeared as a promising inexpensive alternative to the traditional silicon-based solar cells, DSSCs have attracted a considerable amount of experimental and theoretical interest. In contrast with silicon-based solar cells, DSSCs use different components for the light-harvesting and transport functions, which allow researchers to fine-tune each material and, under ideal conditions, to optimize their overall performance in assembled devices. Because of the variety of elementary components present in these cells and their multiple possible combinations, this task presents experimental challenges. The photoconversion efficiencies obtained up to this point are still low, despite the significant experimental efforts spent in their optimization. The development of a low-cost and efficient computational protocol that could qualitatively (or even quantitatively) identify the promising semiconductors, dyes, and electrolytes, as well as their assembly, could save substantial experimental time and resources. In this Account, we describe our computational approach that allows us to understand and predict the different elementary mechanisms involved in DSSC working principles. We use this computational framework to propose an in silico route for the ab initio design of these materials. Our approach relies on a unique density functional theory (DFT) based model, which allows for an accurate and balanced treatment of electronic and spectroscopic properties in different phases (such as gas, solution, or interfaces) and avoids or minimizes spurious computational effects. Using this tool, we reproduced and predicted the properties of the isolated components of the DSSC assemblies. We accessed the microscopic measurable characteristics of the cells such as the short circuit current (J(sc)) or the open circuit voltage (V(oc)), which define the overall photoconversion efficiency of the cell. The absence of empirical or material-related parameters in our approach should allow for its wide application to the optimization of existing devices or the design of new ones.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ar200327wDOI Listing
August 2012

What is the "best" atomic charge model to describe through-space charge-transfer excitations?

Phys Chem Chem Phys 2012 Apr 16;14(16):5383-8. Epub 2012 Mar 16.

CEISAM, UMR CNRS 6230, BP 92208, Université de Nantes, 2, Rue de la Houssinière, 44322 Nantes, Cedex 3, France.

We investigate the efficiency of several partial atomic charge models (Mulliken, Hirshfeld, Bader, Natural, Merz-Kollman and ChelpG) for investigating the through-space charge-transfer in push-pull organic compounds with Time-Dependent Density Functional Theory approaches. The results of these models are compared to benchmark values obtained by determining the difference of total densities between the ground and excited states. Both model push-pull oligomers and two classes of "real-life" organic dyes (indoline and diketopyrrolopyrrole) used as sensitisers in solar cell applications have been considered. Though the difference of dipole moments between the ground and excited states is reproduced by most approaches, no atomic charge model is fully satisfactory for reproducing the distance and amount of charge transferred that are provided by the density picture. Overall, the partitioning schemes fitting the electrostatic potential (e.g. Merz-Kollman) stand as the most consistent compromises in the framework of simulating through-space charge-transfer, whereas the other models tend to yield qualitatively inconsistent values.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c2cp40261kDOI Listing
April 2012

A Qualitative Index of Spatial Extent in Charge-Transfer Excitations.

J Chem Theory Comput 2011 Aug 13;7(8):2498-506. Epub 2011 Jul 13.

LECIME, Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris-Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

With the aim of defining the spatial extent associated to an electronic transition, of particular relevance in the case of charge-transfer (CT) excitations, a new index, evaluated only from the computed density for the ground and excited state, is here derived and tested on a family of molecules that can be considered as prototypes of push-pull chromophores.The index (DCT) allows to define the spatial extent associated to a given transition as well as the associated fraction of electron transferred. By definition of centroids of charges associated to the density increase and depletion zones upon excitation, a qualitative and easy to visualize measure of the spatial extent of the donor and the acceptor moieties within a given molecular system is also given. Finally, an index (t) allowing to define the presence eventually pathologic CT transitions for time-dependent density functional theory treatment in conjunction with standard generalized gradient approximation or hybrid functional, that is through space CT, is disclosed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ct200308mDOI Listing
August 2011

Theoretical procedure for optimizing dye-sensitized solar cells: from electronic structure to photovoltaic efficiency.

J Am Chem Soc 2011 May 4;133(20):8005-13. Epub 2011 May 4.

Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, UMR 7575 CNRS, Ecole Nationale Supérieure de Chimie de Paris-Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

A step-by-step theoretical protocol based on density functional theory (DFT) and time-dependent DFT at both the molecular and periodic levels is proposed for the design of dye-sensitized solar cell (DSSC) devices including dyes and electrolyte additives. This computational tool is tested with a fused polycyclic pyridinium derivative as a novel dye prototype. First, the UV-vis spectrum of this dye alone is computed, and then the electronic structure of the system with the dye adsorbed on an oxide semiconductor surface is evaluated. The influence of the electrolyte part of the DSSC is investigated by explicitly taking into account the electrolyte molecules co-adsorbed with the dye on the surface. We find that tert-butylpyridine (TBP) reduces the electron injection by a factor of 2, while lithium ion increases this injection by a factor of 2.4. Our stepwise protocol is successfully validated by experimental measurements, which establish that TBP divides the electronic injection by 1.6 whereas Li(+) multiplies this injection by 1.8. This procedure should be useful for molecular engineering in the field of DSSCs, not only as a complement to experimental approaches but also for improving them in terms of time and resource consumption.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja201944gDOI Listing
May 2011

Acetylacetone, an interesting anchoring group for ZnO-based organic-inorganic hybrid materials: a combined experimental and theoretical study.

Langmuir 2011 Apr 22;27(7):3442-50. Epub 2011 Feb 22.

Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

Acetylacetone (acacH) adsorption on ZnO (10-10) surface has been studied by a theoretical periodic approach using density functional theory. Two dissociative adsorption modes were investigated and compared to the most stable adsorption mode of formic acid. Acetylacetone appears as a suitable anchoring group for hybrid materials, with adsorption energies of the same order of magnitude as formic acid. IR spectra of the acac/ZnO systems were computed in order to determine the spectral signature of adsorption and, possibly, of each adsorption mode to follow the coordination of acac on ZnO at the experimental level. The results have been compared to Fourier transform infrared (attenuated total reflection-IR) experimental spectra. The present investigation points out the interest of acetylacetone as an anchoring group for the development of new ZnO-based functionalized hybrid layers for corrosion protection, light emitting diodes, photocatalytic systems, and dye-sensitized solar cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/la103634vDOI Listing
April 2011

Effect of solvent and additives on the open-circuit voltage of ZnO-based dye-sensitized solar cells: a combined theoretical and experimental study.

Phys Chem Chem Phys 2010 Nov 15;12(44):14710-9. Epub 2010 Oct 15.

LECIME, Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris-Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

We have investigated the role of electrolyte composition, in terms of solvent and additive, on the open-circuit voltage (V(oc)) of ZnO-based dye-sensitized solar cells (DSSCs) using a combined experimental and theoretical approach. Calculations based on density functional theory (DFT) have been performed in order to describe the geometries and adsorption energies of various adsorbed solvents (nitromethane, acetonitrile and dimethylformamide) and p-tert-butylpyridine (TBP) (modeled by methylpyridine) on the ZnO (100) surface using a periodic approach. The densities of states (DOS) have been calculated and the energy position of the conduction band edge (CBE) has been evaluated for the different molecules adsorbed. The effect of the electrolyte composition on the standard redox potential of the iodide/triiodide redox couple has been experimentally determined. These two data values (CBE and standard redox potential) allowed us to determine the dependence of V(oc) on the electrolyte composition. The variations determined using this method were in good agreement with the measured V(oc) for cells made of electrodeposited ZnO films sensitized using D149 (indoline) dye. As in the case of TiO(2)-based cells, a correlation of V(oc) with the donor number of the adsorbed species was found. The present study clearly points out that both the CBE energy and the redox potential variation are important for explaining the experimentally observed changes in the V(oc) of DSSCs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c004358cDOI Listing
November 2010

Photophysical properties of 8-hydroxyquinoline-5-sulfonic acid as a function of the pH: a TD-DFT investigation.

J Phys Chem A 2010 May;114(18):5932-9

Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

Time dependent density functional theory (TD-DFT) in conjunction with a hybrid exchange correlation functional (PBE0) were applied to characterize the photophysical behavior of the 8-hydroxyquinoline-5-sulfonic acid (8-HQS) in solution as a function of the pH. In particular, absorption and emission spectra of each species as well as their relative stability in the first excited state were computed. From these calculations it is possible to directly derive quantities otherwise hardly experimentally accessible such as excited state acidic dissociation constants (pK(a)*) and corresponding distribution diagrams at the excited state. These two latter quantities were determined by first principles from the relative stabilities of the species at the excited state computed at the TD-DFT level. Consequently, the evolution of the absorption and emission spectral properties of 8-HQS as a function of the pH could be fully simulated from first principles. Finally, insights on energetics and the mechanism of the phototautomerization reaction supposed to be responsible for the absence of fluorescence of the 8-HQS molecule were derived from the calculations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jp1014498DOI Listing
May 2010

A TD-DFT investigation of ground and excited state properties in indoline dyes used for dye-sensitized solar cells.

Phys Chem Chem Phys 2009 Dec 20;11(47):11276-84. Epub 2009 Oct 20.

LECIME, Laboratoire d'Electrochimie, Chimie des Interfaces et Modélisation pour l'Energie, CNRS UMR-7575, Ecole Nationale Supérieure de Chimie de Paris-Chimie ParisTech, 11 rue P. et M. Curie, 75231 Paris Cedex 05, France.

The ground and excited state properties of three indoline dyes, namely D102, D131 and D149, especially designed for dye sensitized solar cell (DSC) applications have been studied by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT) and compared with experimental absorption and fluorescence spectra. By comparison, insight on the behavior of a related dye (D205) is also given. Beside the good agreement between the computed and experimental spectra further proving the accuracy of the method used, that is, a hybrid (here PBE0) exchange correlation functional in conjunction with a polarizable continuum solvent (PCM) model and a medium size basis set, the calculations allow new insights into the electronic structure of this family of indolines, and in particular the electronic and geometrical structure at the first excited state. Possible insights on the optimization of dyes for photovoltaics applications, as well as warnings on the extrapolation of isolated dye properties towards cells behavior are given.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/b914626aDOI Listing
December 2009
-->