Multipodal Au-C grafting of calix[4]arene molecules on gold nanorods.

The interface robustness and spatial arrangement of functional molecules on metallic nanomaterials play a key part in the potential applications of functional nano-objects. The design of mechanically stable and electronically coupled attachments with the underlying metal is essential to bring specific desirable properties to the resulting hybrid materials. In this context, rigid multipodal platforms constitute a unique opportunity for the controllable grafting of functionality.

Radical and diradical states of bis(molybdenocene dithiolene) complexes.

The synthesis and characterization of two bis(dithiolene) proligands involving heteroatomic linkers such as 1,4-dithiine and dihydro-1,4-disiline between the two protected dithiolene moieties are described. Two bimetallic complexes involving these heteroatomic bridges between two redox active bis(cyclopentadienyl)molybdenum dithiolene moieties have been synthesized and characterized by electrochemistry, spectroelectrochemistry, and their properties rationalized with (TD-)DFT. Cyclic voltammetry experiments show sequential oxidation of the two redox centers with Δ values between successive one-electron transfers varying according to the nature of the bridge.

Threading a Linear Molecule Through a Macrocycle Thanks to Boron: Optical Properties of the Threaded Species and Synthesis of a Rotaxane.

Two BODIPYs and two boron β-diketonates were threaded through a macrocycle bearing a 2,2'-biphenol unit, showing thus the ability of boron to act as a gathering atom. The new threaded species were characterized by 1D and 2D NMR spectroscopy as well as by X-ray crystallography for one of them and their properties rationalized with quantum chemistry to unravel the vibronic contributions. The BODIPYs exhibited interesting fluorescence features with quantum yields up to 91 % and enhanced photostability compared to their non-threaded homologues.

Styrylpyrimidine chromophores with bulky electron-donating substituents: experimental and theoretical investigation.

Styrylpyrimidines with bulky 9,9-dimethylacridan, phenoxazine and phenothiazine electron-donating fragments were designed. Thermally activated delayed fluorescence (TADF) properties were expected for these structures. These chromophores exhibit peculiar emission properties.

Kinetic Delay in Cooperative Supramolecular Polymerization by Redefining the Trade-Off Relationship between H-Bonds and Van der Waals/π-π Stacking Interactions.

We here present how rebalancing the interplay between H-bonds and dispersive forces (Van der Waals/π-π stacking) may induce or not the generation of kinetic metastable states. In particular, we show that extending the aromatic content and favouring the interchain VdW interactions causes a delay into the cooperative supramolecular polymerization of a new family of toluene bis-amide derivatives by trapping the metastable inactive state.

A Bimetallic Benzene-1,2,4,5-Tetrathiolate (btt) Molybdenocene Complex Cp Mo(btt)MoCp : Radical and Diradical States.

Benzene-1,2,4,5-tetrathiolate (btt) has been used as a bridging ligand to prepare a redox active (molybdenocene dithiolene)-based bimetallic complex Cp Mo(btt)MoCp , which exhibits four successive electron transfers up to the tetracation. Spectro-electrochemical investigations together with DFT and TD-DFT calculations evidence that the two electroactive MoS C metallacycles are electronically coupled in the monocationic as in the dicationic state. Two salts of the dication [Cp Mo(btt)MoCp ] have been structurally characterized with PF and HSO counterions, showing different chair or boat conformations associated with variable folding angles of the two MoS C metallacycles along the S-S hinge.

Evaluation of tight-binding DFT performance for the description of organic photochromes properties.

Photochromic molecules are widely studied and developed for their many potential applications. To optimize the required properties through theoretical models, a considerable chemical space is to be explored, and their environment in devices is to be accounted for..

Al(III) and Ga(III) Bisphenolate Azadipyrromethene-Based "NO" Complexes as Efficient NIR-Fluorophores.

Aza-boron-dipyrromethenes (Aza-BODIPYs) are an increasingly studied class of fluorophores. They can be seen as an azadipyrromethene ("aza-DIPY") ligand rigidified by a metalloid, a boron atom. Based on this idea, a series of complexes of group 13 metals (aluminum and gallium) have been synthesized and characterized.

Möbius Zn -Hexaphyrins Bearing a Chiral Coordinating Arm: A Chiroptical Switch Featuring P/M Twist Inversion Controlled by Achiral Effectors.

By their conformational flexibility, Möbius aromatic hexaphyrins provide a dynamic chirality attractive to develop stimuli responsive systems such as chiroptical switches. A regular [28]hexaphyrin has been equipped with a chiral coordinating arm to achieve transfer of chirality from a fix stereogenic element to the dynamic Möbius one. The arm allows straightforward formation of labile monometallic Zn complexes with an exogenous ligand, either a carboxylato or an amino with opposite inwards/outwards orientations relative to the Möbius ring.

Photoinduced charge-transfer in chromophore-labeled gold nanoclusters: quantum evidence of the critical role of ligands and vibronic couplings.

The electron flow between a metallic aggregate and an organic molecule after excitation with light is a crucial step on which hybrid photovoltaic nanomaterials are based. So far, designing such devices with the help of theoretical approaches has been heavily limited by the computational cost of quantum dynamics models able to track the evolution of the excited states over time. In this article, we present the first application of the time-dependent density functional tight-binding (TD-DFTB) method for an experimental nanometer-sized gold-organic system consisting of a hexyl-protected Au cluster labelled with a pyrene fluorophore, in which the fluorescence quenching of the pyrene is attributed to the electron transfer from the metallic cluster to the dye.

Push-Pull (Iso)quinoline Chromophores: Synthesis, Photophysical Properties, and Use for White-Light Emission.

The photophysical properties of a series of conjugated push-pull (iso)quinolines were studied. The compounds were synthesized by well-established and straightforward methodologies. The materials exhibited not only emission solvatochromism in a variety of nonpolar solvents, but also tunable halochromism.

Branching effect on the linear and nonlinear optical properties of styrylpyrimidines.

This contribution aims at investigating the branching effect on the steady state, time resolved fluorescence and two-photon absorption (2PA) properties of dimethylamino and diphenylamino substituted styrylpyrimidine derivatives, by means of a combined experimental and theoretical study. In contrast to classical branched molecules with a triphenylamine central core and electron accepting groups at the periphery, here, branched molecules with reverse topology and different symmetries are examined, namely a styrylpyrimidine group is used as the electron withdrawing core and dimethylamino or diphenylamino donors are incorporated at the periphery. Besides, compared to the great majority of existing branched systems, the herein studied molecules do not have C3 symmetry.

Performances of Density Functional Tight-Binding Methods for Describing Ground and Excited State Geometries of Organic Molecules.

We present a benchmark of the performances of the density functional tight-binding model (DFTB) and its time-dependent counterpart (TD-DFTB) in describing both the ground state (GS) and excited state (ES) geometries of a panel of 30 organic molecules. Thanks to high-level wave function reference calculations, we are able to quantitatively assess the strengths and weaknesses of four DFTB models, using either second- or third-order self-consistent charge procedures, as well as different sets of parameters. The performances of the different DFTB models are found to be largely dependent on the type of bond considered, but the global mean absolute error remains acceptable for such "cheap" calculations, as it slightly exceeds the one obtained with DFT (PBE and B3LYP) or CC2 models for the GS of the same set of compounds.

A Blue Diketopyrrolopyrrole Sensitizer with High Efficiency in Nickel-Oxide-based Dye-Sensitized Solar Cells.

We prepared a series of four new diketopyrrolopyrroles (DPPs)-based sensitizers that exhibit high-molar extinction coefficients, extended absorption into the long wavelengths, and well-suited photoredox properties to act as sensitizers in p-type dye-sensitized solar cells (p-DSSCs). These new DPP dyes, composed of a thienyl DPP core, are substituted on one end either by a thiophene carboxylic (Th) or a 4,4'-[(phenyl)aza]dibenzoic acid as anchoring group and, on the other extremity, either by a proton or a naphthalene diimide (NDI) moiety. These new dyes were completely characterized by absorption and emission spectroscopy along with electrochemistry and they were modeled by time-dependent DFT (TD-DFT) quantum chemical calculations.

Is energy transfer limiting multiphotochromism? answers from ab initio quantifications.

Dithienylethenes (DTEs) can be assembled to form supramolecular multiphotochromic systems that are highly functional molecular architectures of potential interest for building complex optoelectronic devices. Yet even simple DTE dimers relying on an organic linker may suffer from a partial photoactivity, i.e.

Investigating the properties of PODIPYs (phosphorus-dipyrromethene) with ab initio tools.

We investigate with a hybrid SOS-CIS(D)/TD-DFT approach accounting for solvation effects, the structural, electronic and optical properties of recently-proposed PODIPY dyes. Being more soluble in water than the well-known BODIPYs, these new chromogens are particularly appealing, but their characterization remains very limited. It turns out that the selected theoretical protocol could reproduce the experimentally reported differences between PODIPY and BODIPY dyes.

A curve-crossing model to rationalize and optimize diarylethene dyads.

Going from photochromic compounds presenting a single switchable function to multi-addressable photochromic multimers remains an extremely difficult task notably because the interactions of several photochromic units through a linker generally result in a substantial loss of photoactivity. Due to their size and the intrinsic complexity of their electronic structure, coupled photochromes also constitute a fundamental challenge for theoretical chemistry. We present here an effective curve-crossing model that, used in connection with easily accessible data, allows a first understanding of the difficulty to obtain efficient multiphotochromes.

SCC-DFTB parameters for simulating hybrid gold-thiolates compounds.

We present a parametrization of a self-consistent charge density functional-based tight-binding scheme (SCC-DFTB) to describe gold-organic hybrid systems by adding new Au-X (X = Au, H, C, S, N, O) parameters to a previous set designed for organic molecules. With the aim of describing gold-thiolates systems within the DFTB framework, the resulting parameters are successively compared with density functional theory (DFT) data for the description of Au bulk, Aun gold clusters (n = 2, 4, 8, 20), and Aun SCH3 (n = 3 and 25) molecular-sized models. The geometrical, energetic, and electronic parameters obtained at the SCC-DFTB level for the small Au3 SCH3 gold-thiolate compound compare very well with DFT results, and prove that the different binding situations of the sulfur atom on gold are correctly described with the current parameters.

Toward an Enhancement of the Photoactivity of Multiphotochromic Dimers Using Plasmon Resonance: A Theoretical Study.

Building dimers of organic photochromic compounds paves the way to multifunctional switches, but such architectures often undergo partial photoreactivity only. Combining photochromism of molecules and plasmon resonance of gold nanoparticles (NPs) is known to affect the photochromism of monomers, yet the impact on multimers remains unknown. Here we propose a theoretical study of dimers of dithienylethenes by the mean of a hybrid calculation scheme (discrete-interaction model/quantum mechanics).

Designing efficient photochromic dithienylethene dyads.

Aiming at designing more efficient multiphotochromes, we investigate with the help of tools the impact of the substitution on a series of dimers constituted of two dithienylethene (DTE) moieties, strongly coupled to each other through an ethynyl linker. The electronic structure and the optical properties of a large panel of compounds, substituted on different positions by various types of electroactive groups, have been compared with the aim of designing a dyad in which the three possible isomers (open-open, closed-open, closed-closed) can be reached. We show that appending the reactive carbons atoms of the DTE core with electroactive groups on one of the two photochromes allows cyclisation to be induced on a specific moiety, which leads to the formation of the desired closed-open isomer.

Multiphotochromic molecular systems.

Molecular systems encompassing more than one photochromic entity can be used to build highly functional materials, thanks to their potential multi-addressability and/or multi-response properties. Over the last decade, the synthesis and spectroscopic and kinetic characterisation as well as the modeling of a wide range of multiphotochromes have been achieved in a field that is emerging as a distinct branch of photochemistry. In this review, we provide an overview of the available multiphotochromic compounds which use a variety of photoactive building blocks, e.

A DFT study of a new class of gold nanocluster-photochrome multi-functional switches.

With the help of a computational scheme combining molecular dynamics, DFT and TD-DFT methods, the conformational, electronic and optical properties of a new class of hybrid compounds where a photochromic molecule belonging to the dithienylethene family (DTE) is covalently linked to a Au25 nanocluster (gold nanocluster or GNC) are investigated. We compare two types of hybrid GNC-DTE systems where the aromatic linker between the metallic and the DTE moieties is either a phenyl or a thiophene ring. By examining the perturbation of the DTE electronic structure after grafting upon the GNC, we show that the hybrid system with a phenyl linker should preserve its photochromic activity.

Density functional theory study of the conformation and optical properties of hybrid Au(n)-dithienylethene systems (n = 3, 19, 25).

We present a theoretical study of Aun-dithienylethene hybrid systems (n = 3, 19, 25), where the organic molecule is covalently linked to a nanometer-scaled gold nanoparticle (NP). We aim at gaining insights on the optical properties of such photochromic devices and proposing a size-limited gold aggregate model able to recover the optical properties of the experimental system. We thus present a DFT-based calculation scheme to model the ground-state (conformation, energetic parameters) and excited-state properties (UV-visible absorption spectra) of this type of hybrid systems.

Ethylenedithio-tetrathiafulvalene-helicenes: electroactive helical precursors with switchable chiroptical properties.

Electroactive fused ethylenedithio-tetrathiafulvalene-[4]helicene and -[6]helicenes have been synthesized through a strategy that involved the preparation of 2,3-dibromo-helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single-crystal X-ray analysis, are 22.7° and 50.