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The second hyperpolarizabilities (γ) of the stilbene molecular switch in its trans and cis forms have been calculated using quantum chemistry methods to address their third-order nonlinear optical contrasts, to assess the reliability of lower-cost DFT methods, and to make comparisons with experiments. First, the reference CCSD(T) method shows that trans-stilbene presents a γ‖ value twice larger than its cis isomer (its γTHS value is 2.7 times larger). Among more cost-effective methods, reliable results are obtained at MP2 as well as with DFT, provided the CAM-B3LYP or ωB97X-D XCFs are employed. Supplementary DFT calculations have investigated the relationships between the accuracy of the exchange–correlation functionals, the fulfillment of Koopmans' theorem, and the delocalization error, and they demonstrated that satisfying Koopmans' theorem is not the condition for the best accuracy but that functionals with small delocalization errors are generally efficient. Using the selected CAM-B3LYP, large γ enhancements by about 70% (trans-stilbene) and 50% (cis-stilbene) have been evidenced when accounting for solvent effects using an implicit solvation model (IEFPCM), even for apolar solvents. Then, the frequency dispersion of the γ responses has been described using Bishop polynomial expansions, allowing comparisons with a broad set of experimental data. To a certain extent, no systematic agreement between the calculations and the measured values was found. On the one hand, the agreement is satisfactory for the γ(−ω;ω,−ω,ω) quantities, provided that the dominant vibrational contribution is taken into account. On the other hand, the agreement is poor for the γ(−2ω;ω,ω,0) and γ(−3ω;ω,ω,ω) quantities, while some inconsistencies between experimental values are also highlighted. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical (NLO) responses of a donor-acceptor stenhouse adduct (DASA) are investigated by using a computational approach combining molecular dynamics simulations and density functional theory (DFT) calculations. Specific force fields for the open and closed photoswitching forms are first parameterized and validated according to the Joyce protocol, in order to finely reproduce the geometrical features and potential energy surfaces of both isomers in chloroform solution. Then, DFT calculations are performed on structural snapshots extracted at regular time steps of the MD trajectories to address the influence of the thermalized conformational dynamics on the NLO responses related to hyper-Rayleigh scattering (HRS) experiments. We show that accounting for the structural dynamics largely enhances the HRS hyperpolarizability (βHRS) compared to DFT calculations considering solely equilibrium geometries, and greatly improves the agreement with experimental measurements. Furthermore, we show that the NLO responses of the NLO-active open form are correlated with the bond order alternation along the triene bridge connecting the donor and acceptor moieties, which is rationalized using simple essential state models. [ABSTRACT FROM AUTHOR]

Due to their versatility and easy processing, Surface-Anchored Metal–Organic Frameworks (SurMOFs) have gained interest in recent times as promising electrochromic thin films. Herein a step forward in their use and characterization was achieved thanks to the integration of {Zn2(PDICl4)2} SurMOFs in a multi-layer electrochromic device (ECD), based on a membrane-like electrolyte. The optical and electrochemical properties of the ECD were fully characterized, revealing a two-step reduction process localized on the organic ligand and involving subsequent near infra-red (NIR) and cyan absorbing states, leading to optical modulation of the films. The species responsible for this absorption were isolated and identified in the reduced states. In parallel to experimental characterization, quantum chemistry was successfully used to investigate the structure–property relationship of the SurMOF, revealing additional information regarding the structure and the local environment of the electrochromic ligand. [ABSTRACT FROM AUTHOR]

This work reports an investigation of the second-order NLO properties of two isomer series of X-shaped pyrazine derivatives, by means of HRS measurements and DFT calculations. The systems differ in the relative position of the donor and acceptor substituents with respect to the axis formed by the nitrogen atoms of the central pyrazine ring. Although the magnitude of the second harmonic signal is similar, HRS measurements revealed that the anisotropy of the NLO response strongly differs in the two chromophore series, the one of the 2,3-isomers being strikingly dipolar, while the one of the 2,6-isomers is mostly octupolar. The experimental observations are well supported by DFT calculations. In particular, the sum-over-states approach allows us to rationalize the different NLO anisotropies observed in the two isomer series through a detailed analysis of the symmetry of the low-lying excited states. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical properties of four series of amphiphilic cationic chromophores involving different push–pull extremities and increasingly large polyenic bridges have been investigated both experimentally, by means of electric field induced second harmonic (EFISH) generation, and theoretically, using a computational approach combining classical molecular dynamics (MD) and quantum chemical (QM) calculations. This theoretical methodology allows to describe the effects of structural fluctuations on the EFISH properties of the complexes formed by the dye and its iodine counterion, and provides a rationale to EFISH measurements. The good agreement between experimental and theoretical results proves that this MD + QM scheme constitutes a useful tool for a rational, computer-aided, design of SHG dyes. [ABSTRACT FROM AUTHOR]

Silicon phthalocyanine (SiPc) derivatives have recently emerged as promising materials for n-type organic thin-film transistors (OTFTs) with the ability to be fabricated either by solid state or solution processes through axial functionalization. Among those, bis(tri-n-propylsilyl oxide) SiPc ((3PS)2-SiPc) is unique as it can be processed by sublimation, while being soluble enough for solution processing. In this work, the charge transport properties of (3PS)2-SiPc and its polymorphic forms were studied through Kinetic Monte Carlo (KMC) simulations and density functional theory (DFT) calculations along with the characterization of (3PS)2-SiPc in n-type OTFTs fabricated by physical vapour deposition (PVD) and spin coating. Post-deposition thin-film characterization by X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning transmission X-ray microscopy (STXM) was used to assess film morphology and microstructure in relation to the electrical performance of OTFTs. The differences in film formation by PVD and solution fabrication had little effect on OTFT performance with comparable field-effect mobility and threshold voltage ranging between 0.01–0.04 cm2 V−1 s−1 and 18–36 V respectively. Consistent charge transport properties of (3PS)2-SiPc OTFTs achieved at different fabrication conditions highlights the processing versatility of this material. [ABSTRACT FROM AUTHOR]

Owing to their intense emission, low toxicity and solubility in aqueous medium, fluorescent organic nanoparticles (FONs) have emerged as promising alternatives to inorganic ones for the realization of exogenous probes for bioimaging applications. However, the intimate structure of FONs in solution, as well as the role played by intermolecular interactions on their optical properties, remains challenging to study. Following a recent Second-Harmonic Scattering (SHS) investigation led by two of us [Daniel et al., ACS Photonics, 2015, 2, 1209], we report herein a computational study of the structural organization and second-order nonlinear optical (NLO) properties of FONs based on dipolar chromophores incorporating a hydrophobic triphenylamine electron-donating unit and a slightly hydrophilic aldehyde electron-withdrawing unit at their extremities. Molecular dynamics simulations of the FON formation in water are associated with quantum chemical calculations, to provide insight into the molecular aggregation process, the molecular orientation of the dipolar dyes within the nanoparticles, and the dynamical behavior of their NLO properties. Moreover, the impact of intermolecular interactions on the NLO responses of the FONs is investigated by employing the tight-binding version of the recently developed simplified time-dependent density functional theory (sTD-DFT) approach, allowing the all-atom quantum mechanics treatment of nanoparticles. [ABSTRACT FROM AUTHOR]

The geometrical structures, relative Z–E energies, and second-order nonlinear responses of a collection of azobenzene molecules symmetrically substituted in the meta-position with functional groups of different bulkiness are investigated using various ab initio and density functional approximations. We show that RI-MP2 and RI-CC2 approximations provide very similar geometries and relative energies and evidence that London dispersion interactions existing between bulky meta-substituents stabilize the Z conformer. The ωB97X-D exchange–correlation functional provides an accurate description of these effects and gives a good account of the nonlinear optical response of the molecules. We show that density functional approximations should include no less than 50% of Hartree–Fock exchange to provide accurate hyperpolarizabilities. A property–structure analysis of the azobenzene derivatives reveals that the main contribution to the first hyperpolarizability comes from the azo bond, but phenyl meso-substituents can enhance it. [ABSTRACT FROM AUTHOR]

We report the first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons. Rheology, microscopy, and spectroscopy studies reveal that the fluorous sodium L -prolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin is about 1000 times longer than in pure water. [ABSTRACT FROM AUTHOR]

The second-order nonlinear optical responses of a series of recently designed dipolar merocyanines are investigated using the 2006 Minnesota family of hybrid exchange–correlation functionals (XCFs), as well as the LC-BLYP, ωB97XD and CAM-B3LYP long-range (LR) corrected XCFs. The performance of these different levels of approximation is discussed in regard to reference second-order Møller–Plesset calculations and experimental data obtained from Hyper-Rayleigh Scattering (HRS) measurements. Particular focus is given to the influence of the amount of exact Hartree–Fock exchange included in the XCF on the magnitude of the static HRS responses, as well as to the impact of tuning the range-separation parameter in LR-XCFs, according to a system-specific nonempirical procedure. Frequency dispersion effects are also investigated, as well as their crucial role in the comparison between theoretical and experimental data. [ABSTRACT FROM AUTHOR]

In an effort to gain a fundamental understanding of the electromechanical response in high mobility crystalline organic semiconductors, we have investigated the uniaxial strain–mobility relationships in rubrene and benzothienobenzothiophene crystals. Elastic moduli and Poisson ratios of the materials are evaluated and the strain mobility response of these materials is rationalized using the effective masses and electronic couplings in the framework of hopping and band transport models, giving consistent results. The microscopic origin of the response is investigated in relation to the strain induced variations in the inter- and intra-molecular degrees of freedom. We demonstrate that the strain applied along one of the crystallographic directions in these materials does not only induce mobility variations along the same direction, but also along the other crystallographic directions that are mechanically coupled with large Poisson ratios. A rational design of electronic devices could therefore benefit from the efficient exploitation of this anisotropic strain mobility response in relation to the inherent crystalline anisotropy. [ABSTRACT FROM AUTHOR]

We report the first investigation of the second-order nonlinear optical (NLO) properties of donor–acceptor Stenhouse adducts (DASAs), an emerging class of colored photochromes that undergo photoswitching with visible light to a colorless form. By using time-dependent density functional theory, we provide insights into the relationships linking the nature of the chemical substituents to the amplitude and contrasts of the NLO response. Solvent and frequency dispersion effects are also analyzed. The calculations predict that DASAs behave as high contrast NLO switches, a finding that extends their potential applications to photo-responsive NLO materials and devices. [ABSTRACT FROM AUTHOR]

In this work we present the synthesis, characterization and theoretical investigation of three boron-difluoride-curcuminoid derivatives and their covalent homodimers chemically linked through a polymethylenic chain. Low-lying electronic excited states and photophysical properties of the monomeric species have been described as the convolution of different donor–acceptor intramolecular excitations. Covalent dimers in solution can present open or folded structural conformations. Analysis of absorption profiles and computational results allow to identify the factors that control the relative stability of the two forms and rationalize its dependence with the solvent polarity. Interestingly, the strong electronic coupling in the folded forms results in low-lying excitations with sizable mixings of intra- and inter-chromophoric contributions, which cannot be described by means of the Kasha model of interacting chromophores. Our study demonstrates how decomposition of the computed excitations in terms of diabatic states can be extremely valuable in order to identify and quantify the nature of electronic transitions in the presence of several electron donor and acceptor fragments. [ABSTRACT FROM AUTHOR]

A computational approach combining molecular dynamic simulations and density functional theory (DFT) calculations is implemented to evaluate the second-order nonlinear optical (NLO) responses of photoresponsive self-assembled monolayers (SAMs) based on indolino–oxazolidine molecular switches. These numerical simulations provide a complete atomistic picture of the morphology of the SAMs, revealing a high degree of positional disorder and an almost isotropic orientation of the chromophores. Subsequent DFT calculations, carried out to evaluate the average first hyperpolarizability of indolino–oxazolidine switches within the SAM, predict that the structural disorder does not significantly reduce the NLO contrast compared to that of the isolated molecules. Chromophores in the SAM can assume a limited number of specific conformations, due to the high rotational barrier that characterize the conjugated bonds along the indolino/oxazolidine-dyene-thiophene sequence. A notable exception is the rotation about the thiophene–thioalkyl bond, which is not only almost free, but also strongly correlated with the magnitude of the first hyperpolarizability. Controlling this rotation by chemical design could thus be a viable strategy to optimize the SAMs NLO response and the performance of photoresponsive devices based on indolino/oxazolidine switches. [ABSTRACT FROM AUTHOR]

The study of a [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative decorated with hexyl chains functionalized with hydroxyl end groups is reported. A rapid and inexpensive functionalization of the BTBT in positions 2 and 7 has been developed. This compound is able to self-organize into a lamellar structure through σ–π stacking and van der Waals interactions but also through hydrogen bonding interactions. The hydrogen-bonded network controls the interlamellar region in terms of organization and stability. The liquid-crystal phase and structural changes observed by DSC have been characterized using an original approach combining FTIR and powder XRD measurements as a function of temperature. Thermally evaporated diol based OFETs exhibited good mobilities of up to 0.17 cm2 V−1 s−1 measured under an inert atmosphere but also in ambient air. The diol derivative is considered to be a very promising platform for the design of new functionalized BTBT. [ABSTRACT FROM AUTHOR]

We describe the design, synthesis, and fluorescent profile of two environment-sensitive dyes in which an electron-donating group is conjugated to an electron-accepting unit via a pyrrolo[3,2-b]pyrrole ring system. The maximum emission wavelength (λem) of these donor–donor–acceptor (D–D–A) pyrrolo[3,2-b]pyrroles was found to be very sensitive to the environment (a bathochromic shift of about 100 nm in polar solvents). The longer emission wavelength in polar aprotic as well as hydrophilic solvents compared with that in low-polarity hydrophobic solvents was due to an ICT character of the excited state. The Stokes shift increased in both cases following the polarity differences, reaching ∼7000 cm−1 in MeOH for the compound possessing a cyano group and dimethylamino groups at the periphery. Interestingly, the two-photon absorption responses were also found to be quite sensitive to solvent polarity with an increase by a factor of about 2 on going from an apolar solvent to a highly polar protic or aprotic solvent. [ABSTRACT FROM AUTHOR]

Improving the performance of organic photovoltaic cells requires the individuation of the specific factors limiting their efficiency, by rationalizing the relationship between the chemical nature of the materials, their morphology, and the electronic processes taking place at their interface. In this contribution, we present recent theoretical advances regarding the determination of the energetics and dynamics of charge carriers at organic–organic interfaces, highlighting the role of structural and electrostatic disorder in the separation of electron–hole pairs. The influence of interfacial electrostatic interactions on charge carrier energetics is first illustrated in model aggregates. Then, we review some of our recent theoretical studies in which we combined molecular dynamics, quantum-chemical and classical micro-electrostatic methods to evaluate the energy landscape explored by the mobile charges in the vicinity of donor–acceptor interfaces with realistic morphologies. Finally, we describe the theoretical challenges that still need to be overcome in order to gain a complete overview of the charge separation processes at the molecular level. [ABSTRACT FROM AUTHOR]

The contrast of second-order nonlinear optical response in the dihydroazulene (DHA)-vinylheptafulvene (VHF) equilibrium has been investigated as a function of the nature of the substituent (R) on the phenyl ring by means of quantum chemistry calculations including electron correlation, frequency dispersion, and solvent effects. By considering the hyper-Rayleigh scattering (HRS) response, the contrast for R = H and R = CH3between the DHA and VHF forms is larger than 5 while the contrast between the cisand transVHF forms is close to 1. Adding the NH2donor group in paraposition of the phenyl leads to a substantial increase of the HRS first hyperpolarizability of the three forms, which is detrimental to the contrast. Then, in the case of the NO2acceptor group, a contrast is recovered because the HRS first hyperpolarizability of the DHA form is about 2–3 times larger than for both VHF forms. These variations of first hyperpolarizability as a function of the substituents as well as the associated contrasts have been explained in terms of donor/acceptor strengths and geometrical parameters. [ABSTRACT FROM AUTHOR]

Due to their versatility and easy processing, Surface-Anchored Metal-Organic Frameworks (SurMOFs) have gained interest in recent times as promising electrochromic thin films. Herein a step forward in their use and characterization was achieved thanks to the integration of {Zn 2 (PDICl 4 ) 2 } SurMOFs in a multi-layer electrochromic device (ECD), based on a membrane-like electrolyte. The optical and electrochemical properties of the ECD were fully characterized, revealing a two-step reduction process localized on the organic ligand and involving subsequent near infra-red (NIR) and cyan absorbing states, leading to optical modulation of the films. The species responsible for this absorption were isolated and identified in the reduced states. In parallel to experimental characterization, quantum chemistry was successfully used to investigate the structure-property relationship of the SurMOF, revealing additional information regarding the structure and the local environment of the electrochromic ligand.

Structural integration of two synthetic water soluble receptors for Ca 2+ and Mg 2+ , namely 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and o-aminophenol-N,N,O-triacetic acid (APTRA), respectively, gave novel di- and tritopic ionophores (1 and 2). As Mg 2+ and Ca 2+ cannot be simultaneously complexed by the receptors, allosteric control of complexation results. Potentiometric measurements established stepwise protonation constants and showed high affinity for Ca 2+ (log K = 6.08 and 8.70 for 1 and 2, respectively) and an excellent selectivity over Mg 2+ (log K = 3.70 and 5.60 for 1 and 2, respectively), which is compatible with magnesium-calcium ion exchange. While ion-exchange of a single Mg 2+ for a single Ca 2+ is possible in both 1 and 2, the simultaneous binding of two Mg 2+ by 2 appears prohibitive for replacement of these two ions by a single Ca 2+ . Ion-binding and exchange was further rationalized by DFT calculations.

Time-dependent Hartree-Fock and Møller-Plesset second-order calculations have been used to unravel the relationships between structure and first hyperpolarizability in spiropyran/merocyanine couples and therefore to design efficient second-order nonlinear optical switching compounds. Large first hyperpolarizabilities for the merocyanine form as well as large contrasts of first hyperpolarizability have been obtained when, on the same species, (i) substituents at R(1) and R(2) positions on the phenolate ring of the merocyanine form are strong acceptor and donor substituents, respectively, (ii) the ethylenic bridge is substituted by donor groups, (iii) the other aromatic part of the system is benzimidazolo rather than indolino or benzothiazolo, and (iv) strong donor substituents are placed on the benzimidazolo moiety.