Namur Institute of Structured Matter

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.

As a group of subject matter experts in X-ray photoelectron spectroscopy (XPS), we write this letter to raise awareness of the epidemic of poor and incorrect materials data analysis in the Literature. This is a chronic and growing problem with very undesirable consequences. This issue may contribute to what has been identified as a “reproducibility crisis”1,2 that was the subject of a recent U.S. National Academies study. We are using XPS as one example of what we observe to be a systemic issue.

Abstract Incorporation of compact spectroscopic near‐infrared (NIR) light detectors into various wearable and handheld devices opens up new applications, such as on‐the‐spot medical diagnostics. To extend beyond the detection window of silicon, i.e., past 1000 nm, organic semiconductors are highly attractive because of their tunable absorption. In particular, organic NIR wavelength‐selective detectors have been realized by incorporating donor:acceptor thin films, exhibiting weak intermolecular charge‐transfer (CT) absorption, into an optical microcavity architecture. In this work, the alkyl side chains of the well‐known PBTTT donor polymer are replaced by alkoxy substituents, hereby redshifting the CT absorption of the polymer:PC 61 BM blend. It is shown that the unique fullerene intercalation features of the PBTTT polymer are retained when half of the side chains are altered, hereby maximizing the polymer:fullerene interfacial area and thus the CT absorption strength. This is exploited to extend the detection range of organic narrow‐band photodetectors with a full‐width‐at‐half‐maximum of 30–38 nm to wavelengths between 840 and 1340 nm, yielding detectivities in the range of 5 × 10 11 to 1.75 × 10 10 Jones, despite the low CT state energy of 0.98 eV. The broad wavelength tuning range achieved using a single polymer:fullerene blend renders this system an ideal candidate for miniature NIR spectrophotometers.

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.

Synthesis and antiproliferative activities of Cu(<sc>ii</sc>) complexes with tridentate Schiff-base ligands containing pyridine and 3,5-halogen substituted phenol moieties were investigated.

To gauge the suitability of an organic dye for thermally activated delayed fluorescence (TADF), its excited state properties are often calculated using density functional theory. For this purpose, the choice of the exchange-correlation (XC) functional is crucial as it heavily influences the quality of the obtained results. In this work, 19 different XC functionals with various amounts of Hartree-Fock (HF) exchange and/or long-range correction parameters are benchmarked versus resolution-of-the-identity second-order coupled cluster (riCC2) calculations for a set of 10 prototype intramolecular donor-acceptor compounds. For the time-dependent density functional theory (TD-DFT) calculations, LC-BLYP(ω = 0.20) and M06-2X are the better performing XC functionals when looking at singlet and triplet excitation energies, respectively. For the singlet-triplet energy gap, LC-BLYP(ω = 0.17), LC-ωPBE(ω = 0.17) and a hybrid LC-BLYP(ω = 0.20)/M06-2X method give the smallest mean average errors (MAEs). Using the Tamm-Dancoff approximation (TD-DFT/TDA), the MAEs are further reduced for the triplet vertical excitation energies and the singlet-triplet energy gaps.

We have investigated the potential as an OLED emitter of a spiro compound with phosphine substituents initially designed as a host layer for triplet emitters.

Boron dipyrromethene (BODIPY) dyes represent a particular class within the broad array of potential photosensitizers. Their highly fluorescent nature opens the door for theragnostic applications, combining imaging and therapy using a single, easily synthesized chromophore. However, near-infrared absorption is strongly desired for photodynamic therapy to enhance tissue penetration. Furthermore, singlet oxygen should preferentially be generated without the incorporation of heavy atoms, as these often require additional synthetic efforts and/or afford dark cytotoxicity. Solutions for both problems are known, but have never been successfully combined in one simple BODIPY material. Here, we present a series of compact BODIPY-acridine dyads, active in the phototherapeutic window and showing balanced brightness and phototoxic power. Although the donor-acceptor design was envisioned to introduce a charge transfer state to assist in intersystem crossing, quantum-chemical calculations refute this. Further photophysical investigations suggest the presence of exciplex states and their involvement in singlet oxygen formation.

Rational, computationally guided, molecular design affords push–pull BODIPY photosensitizers with balanced brightness and phototoxicity for image-guided photodynamic therapy.

Stents are cardiovascular devices used to treat atherosclerosis, and are deployed into narrowed arteries and implanted by expansion to reopen the biological lumen. Nevertheless, complications after implantation are still observed in 10-14% of the implantations. Therefore, functionalizing these devices with active molecules to improve the interfacial effects with the surrounding tissue strongly impacts their success. A plasma-based procedure to directly graft biomolecules to the surface of cobalt chromium alloys, without any polymeric coating, has been recently reported. Assuring the stability of the coating during plastic deformation generated during the implantation whilst avoiding the corrosion of the surface is crucial. This study explores different surface treatments to be used as a pre-treatment for this novel procedure. The effects of (i) electropolishing, (ii) thermal treatments, and (iii) the plasma immersion ion implantation of oxygen on the chemical composition, roughness, wettability and efficiency during the plasma-amination procedure whilst avoiding cracks after deformation, thus maintaining corrosion resistant behaviour, were investigated by XPS, AFM, ToF-SIMS imaging and depth profile, and WCA. Furthermore, the hemocompatibility of the surface and cell viability assays were also performed. Results showed that all of the treatments created a different surface chemical composition: EP mainly of chromium oxide, PIII with a layer of cobalt oxide and TT with a mixture of oxides, as observed by XPS and ToF-SIMS. Moreover, EP was the process that generated a surface with the highest efficiency to amination and the most corrosion resistance among the treatments, and it appeared as the most suitable pre-treatment for stent functionalization.

Volatile Organic Compounds (VOCs) are known to be hazardous and harmful to human health and the environment. In mixtures or during repeated exposures, significant toxicity of these compounds in trace amounts has been revealed. In vitro air-liquid interface approaches underlined the interest in evaluating the impact of repeated VOC exposure and the importance of carrying out a toxicological validation of the techniques in addition to the standard chemical analyses. The difficulties in sampling and measuring VOCs in stationary source emissions are due to both the complexity of the mixture present and the wide range of concentrations. The coupling of VOC treatment techniques results in efficient systems with lower operating energy consumption. Three main couplings are outlined in this review, highlighting their advantages and relevance. First, adsorption-catalysis coupling is particularly valuable by using adsorption and catalytic oxidation regeneration initiated, for example, by selective dielectric heating. Then, several key aspects of the plasma catalysis process, such as the choice of catalysts suitable for the non-thermal plasma (NTP) environment, the simultaneous removal of different VOCs, and the in situ regeneration of the catalyst by NTP exposure, are discussed. The adsorption-photocatalysis coupling technology is also one of the effective and promising methods for VOC removal. The VOC molecules strongly adsorbed on the surface of the photocatalyst can be directly oxidized by the photogenerated hole on the photocatalyst (e.g., TiO2).

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.

We compare two small π-conjugated donor-bridge-acceptor organic molecules differing mainly in the number of thiophene rings in their bridging motifs (1 ring in 1; 2 rings in 2) with the aim of rationalizing the origin of the enhancement in the singlet exciton diffusion coefficient and length of 1 with respect to 2. By combining force field molecular dynamics and micro electrostatic schemes with time-dependent density functional theory and kinetic Monte Carlo simulations, we dissect the nature of the lowest electronic excitations in amorphous thin films of these molecules and model the transport of singlet excitons across their broadly disordered energy landscapes. In addition to a longer excited-state lifetime associated with a more pronounced intramolecular charge-transfer character, our calculations reveal that singlet excitons in 1 are capable of funneling through long-distance hopping percolation pathways, presumably as a result of the less anisotropic shape of the molecule, which favours long-range 3D transport.

A computational study of the magnetically-induced current (MIC) density has been carried out for a variety of ortho fused polycyclic aromatic molecules at the density functional theory level with the gauge including magnetically induced current (GIMIC) method. With this method, the aromatic character of each ring in a homologous series of carbohelicenes with an increasing number of fused benzene rings is assessed and compared with other aromaticity criteria such as the Nucleus Independent Chemical Shift [NICS(0), NICSzz(0)] and Bond Length Alternation (BLA) parameters. All criteria indicate that the two outer rings are the most aromatic ones [i.e. higher induced current, more negative NICS(0) and NICSzz(0) values, and smaller BLA values]. For the large helicenes (n > 10), the current drops along the following four rings and then rises again. Additionally, we have proven that this behavior is not due to a difference of the local magnetic field coming from a difference of orientation of the ring with respect to the external magnetic field (oriented along the helical axis). Upon fusing additional benzene rings to form hexa-peri-hexabenzo[7]helicene, some rings (B, D, and F) are a lot less aromatic (even non-aromatic) than the others. The NICS(0) and NICSzz(0) values exaggerate this behavior because they are all positive values, which is a signature of antiaromaticity. Then, when substituting one, three, or four benzene rings with pyrrole ones to form mono-aza-[7]-helicene, tri-aza-[7]-helicene, and tetra-aza-[7]-helicene, remarkable changes in the electronic structures of the helicenes are observed. Indeed, the induced currents are always smaller in the pyrrole rings than in the benzene ones. This has been further investigated using the streamline and the color map representations, which indicate that the diatropic current density passing through the plane cutting the C-N bonds in the pyrrole rings is stronger but is more localized than the current density passing through the plane cutting the C-C bonds in the benzene rings. This gives a positive but smaller total induced current for the pyrrole rings than for the benzene ones. For these systems, the NICS(0) and even more the NICSzz(0) values are not fully reliable to probe the local aromaticity, contrary to the induced current. Indeed, the NICSzz(0) values for the tri-aza-[7]-helicene molecule range from -14.23 to 1.14 ppm, which cannot lead to the same conclusion as the induced current values (10.03 to 12.87 nA T-1).

A sequential approach combining molecular dynamics and density functional theory calculations has been worked out to unravel the second harmonic generation responses of anion–cation (AC) pairs when they form dimeric aggregates, where the cation is a stilbazolium derivative and the anions range from small inorganic iodide to medium-size organic p-toluenesulfonate. These complexes showed a strong self-aggregation behavior in molecular dynamics simulations within high-concentration conditions and formed stable dimeric aggregates, (AC)2, which can adopt different structural shapes from stacked, Λ, to head-to-head configurations. These various structures are associated with different symmetries, which are shown to modulate the second- and third-order nonlinear optical (NLO) responses. By consolidating the NLO results of this work with those previously obtained for single AC pairs [ J. Chem. Inf. Model. 2020, 60, 4817−4826], we have been able to explain the experimentally observed variations of the electrical-field-induced second harmonic generation (EFISHG) responses of these complexes as a function of concentration [ ChemPhysChem 2010, 11, 495−507]. Moreover, results have highlighted that (i) the second-order contribution, μβ//, dominates the global EFISHG response; (ii) the μβ// responses of dimers are about half of those computed for the parent AC pairs, while the third-order contributions, γ//, are reduced by only 10%; (iii) these distinct trends are ascribed to the formation of dimers adopting mainly Λ and head-to-head shapes, increasing the centrosymmetric character, in comparison to the monomers, a situation in which the second-order response cancels out as well as influences the dipole moment on μβ//; (iv) the presence of a strong amino donor group in the cation enhances the μβ// response by 1 order of magnitude and γ// by about a factor of 2; and finally, (v) dimeric aggregation has similar effects on the hyper-Rayleigh scattering response, βHRS, as on μβ//, while it reduces the one-dimensional character of βHRS. This work constitutes a step forward for the modeling of the NLO responses of AC aggregates in solution.

Understanding the interaction of water and graphene is crucial for various applications such as water purification, desalination, and electrocatalysis. Experimental and theoretical studies have already investigated water adsorption on N- and B-doped graphene. However, there are no reports available that elucidate the influences of the N and B doping content in graphene on the microscopic geometrical structure and the electronic properties of the adsorbed water. Thus, this work is devoted to solving this problem using self-consistent van der Waals density functional theory calculations. The N and B doping contents of 0.0, 3.1, 6.3, and 9.4% were considered. The results showed that the binding energy of water increases almost linearly as a function of doping content at all concentrations for N-doped graphene but below 6.3% for B-doped graphene. In the linear range, the binding energy increases by approximately 30 meV for each increment of the doping ratio. Analyses of the geometric and electronic structures explained the enhancement of the water-graphene interaction with the variation in doping percentage.

Three phenoxazine-π-bridge-benzothiazole dyes are investigated by a joint experimental-computational approach. Depending on the linker, TADF or RTP (also in solution) is observed.

To investigate the effect of chirality and different halogen substituents on the anticancer activity, seven enantiomeric pairs of palladium complexes were synthesized and characterized.

A new strategy is developed to design multi-drug solid forms. Using an inorganic salt as the glue sticking together two different APIs in a "drug-bridge-drug" approach, we successfully created and characterized three different ternary ionic cocrystals (TICCs). The link between binary and ternary ICCs and the importance of reaction stoichiometry was investigated using ternary solid-state phase diagrams. In addition, we highlighted the crucial role of water for the stability of these systems, as well as the impact on solubility compared to the respective parent compounds. We expect the strategy presented here to be applicable to a large series of drug combinations, opening up a promising new way of building multi-drug systems.

Perylene diimide (PDI) dyes are extensively investigated because of their favorable photophysical characteristics for a wide range of organic material applications. Fine-tuning of the optoelectronic properties is readily achieved by functionalization of the electron-deficient PDI scaffold. Here, we present four new donor-acceptor type dyads, wherein the electron donor units - benzo[1,2-b : 4,5-b']dithiophene, 9,9-dimethyl-9,10-dihydroacridine, dithieno[3,2-b : 2',3'-d]pyrrole, and triphenylamine-are attached to the bay-positions of the PDI acceptor. Intersystem crossing occurs for these systems upon photoexcitation, without the aid of heavy atoms, resulting in singlet oxygen quantum yields up to 80 % in toluene solution. Furthermore, this feature is retained when the system is directly irradiated with energy corresponding to the intramolecular charge-transfer absorption band (at 639 nm). Geometrical optimization and (time-dependent) density functional theory calculations afford more insights into the requirements for intersystem crossing such as spin-orbit coupling, dihedral angles, the involvement of charge-transfer states, and energy level alignment.