In this work, we report the design and synthesis of two new organic D-A-π-A dyes endowed with a common benzothiadiazole-dithienosilole (BTD-DTS) central core, and their evaluation as anodic sensitizers in dye-sensitized photoelectrochemical cells (DS-PEC) aimed at molecular hydrogen generation. Both dyes possess a cyanoacrylic acid as acceptor/anchoring group, but present two distinct donor groups bearing substituents of different hydrophilicity. Preliminary density functional theory (DFT) computational investigations indicated that the dyes presented the correct electronic structure and energy levels alignment for their desired application in devices. The compounds were then prepared by means of a concise synthetic sequence featuring a microwave-assisted Stille-Migita cross-coupling as the key step. Following their full spectroscopic and electrochemical characterization, the dyes were then employed to sensitize the nanocrystalline TiO2- or SnO2-based photoanodes of three-electrode DS-PECs, and the corresponding performances in terms of photocurrent production and hydrogen generation, as well as electrode stability, were assessed under several different conditions.

Two new members of the family of NCN -Pt( ii ) complexes have been synthesized. The compounds present new aryl substituents on the pyridine rings and have been deeply characterized, pointing out their high luminescence and QY (89–98%).

The synthesis and characterization of two new complexes, namely Pt(1,3-bis(4-(4-hexyl-2-thienyl)-pyridin-2-yl)-5-mesitylbenzene)Cl and Pt(1,3-bis(4-(4-hexyl-2-thienyl)-pyridin-2-yl)-5-(2-thienyl)benzene)Cl, are reported. Both exhibit luminescence quantum yields approaching unity (Φlum = 0.96–0.99) in the green region of the visible spectrum (534–554 nm) in diluted degassed dichloromethane solution. Similarly to other N^C^N platinum(II) complexes, a broad emission band grows in the deep red region (738–752 nm) upon increasing the concentration, due to the creation of bi-molecular emissive excited states. Interestingly, it appears that the introduction of a 2-thienyl group on the pyridine rings is a route to maintain excellent quantum yields even in concentrated solution. In order to have an insight into the electronic properties of the novel compounds, density functional theory (DFT) and time-dependent (TD)DFT approaches were employed to calculate the molecular geometry, the ground state, the electronic structure and the excited electronic states of the complexes, both as a monomers and dimers in solution.

The second-order nonlinear optical (NLO) properties of the known heteroleptic complex [Cu(1,10-phenanthroline)xantphos][PF6] (complex 1) and the related new complexes [Cu(5-NO2-1,10-phenanthroline)xantphos][PF6] and [Cu(5-NO2-1,10-phenanthroline)(dppe)][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane) (complexes 2 and 3) were investigated in solution by the EFISH (Electric Field-Induced Second Harmonic generation) technique, working at a non-resonant wavelength of 1907 nm. It turned out that they are characterized by large μβ values (957–1100 × 10−48 esu), much higher than that of the Disperse Red One benchmark. Unexpectedly, the homoleptic complex [Cu(2-mesityl-1,10-phenanthroline)2][PF6] (complex 4) shows a similar high second-order NLO response. Quantum chemical calculations based on Density Functional Theory (DFT) methods have been carried out to give insight into the electronic structure of the investigated complexes in relation to NLO properties. This investigation, which represents the first EFISH study on copper(I) complexes, opens a convenient route for the development of low-cost dipolar NLO-active heteroleptic [Cu(P^P)(N^N)][PF6] and homoleptic [Cu(N^N)2][PF6] complexes.

The non-linear optical and antitumoral properties of cis-Ir(N,C-ppy)2(O,O-THC) have previously been established (where ppy and THC are the deprotonated forms of 2-phenylpyridine and tetrahydrocurcumin, respectively). In the present study, this complex is investigated as a green phosphorescent emitter for an OLED fabricated by solution processing. The device efficiency is similar to that of an analogue employing the archetypal complex cis-Ir(N,C-ppy)2(O,O-acac), but shows a higher luminance at low applied voltages (<6 V). In order to explore whether this effect might be observed in the blue region too, a new derivative has been prepared and characterized, namely cis-Ir(N,C-F2ppy)2(O,O-THC) (F2ppyH = 2-(2,4-difluorophenyl)pyridine). It, too, gives an OLED with a particularly high luminance at low voltage, suggesting a beneficial effect of substituting acetylacetonate by tetrahydrocurcuminate.

Reaction of 4-methylphenylacetylide with the known chlorido platinum(II) complex bearing the cyclometalated 1,3-bis(pyridin-2-yl)-4,6-difluoro-benzene ligand afforded a novel alkynyl platinum(II) complex, 1, that was fully characterized by elemental analysis, NMR and UV-visible spectroscopies, by photoluminescence measurements, and by computational modelling. Its structure was determined by X-ray diffraction studies on a single crystal whereas its second-order nonlinear optical (NLO) properties were determined in solution by the Electric-Field Induced Second Harmonic generation method. The novel multifunctional complex 1 is characterized by good luminescence properties, like the related chlorido Pt(II) complex, but by a much higher second-order NLO response.

Substitution of chloride by azide in cyclometalated 5-R-1,3-di(2-pyridyl)-benzene platinum(II) complexes (R = mesityl, methyl or 2-thienyl) leads to novel azido complexes with an intense phosphorescence that is modulated by the nature of R. An increase of the concentration brings about to the formation of aggregates with a red-shifted emission. Furthermore, the presence of the ancillary azido group allows, via i-click reaction, the obtainment of even more emissive 1,2,3-triazole derivatives. The 1,2,3-triazolate of the mesityl and 2-thienyl N C N-Pt(II) complexes were characterized by X-ray diffraction analysis and their photophysical properties were deeply investigated.

While the development of red and green phosphorescent organic light-emitting diodes (OLEDs) has seen rapid progress, that of efficient blue phosphorescent OLEDs remains a challenge. In the present report, the introduction of a bulky substituent on the pyridyl rings of a cycloplatinated 1,3-bis(pyridine-2-yl)-4,6-difluoro-benzene appears as a facile strategy to hinder strong Pt & ctdot;Pt interactions, allowing the fabrication of efficient blue OLEDs. Thus, the preparation and characterization of a chlorido platinum(ii) complex bearing a well-designed new N<^>C<^>N-cyclometalating ligand, namely 1,3-bis(4-mesityl-pyridin-2-yl)-4,6-difluoro-benzene, are reported. Its structure, along with that of the related pro-ligand, is determined by X-ray diffraction studies on a single crystal. The shortest Pt & ctdot;Pt distance is much longer (8.59 & Aring;) than that observed for other N<^>C<^>N-platinum(ii) chlorido complexes including one with the bulky mesityl group on the cyclometalated benzene ring (4.4 & Aring;). This new complex exhibits intense blue phosphorescence (470-471 nm) in dichloromethane solution (Phi lum = 0.97) and in the PMMA film (1 wt% complex, Phi lum = 0.95) whereas red phosphorescence (672 nm) is observed in a neat film (Phi lum = 0.72). Even in the solid state, the novel complex is highly luminescent suggesting that the introduction of mesityl groups on the pyridine rings is a way to inhibit self-quenching both in the PMMA matrix and in neat films. It represents a useful tool for the fabrication of efficient blue OLEDs (8% wt complex) with CIE coordinates (0.13, 0.29) approaching true blue. The molecular geometry, ground state, electronic structure, and excited electronic states of the complex, both as a monomer and dimer aggregate in solution, are calculated using density functional theory (DFT) and time-dependent (TD) DFT approaches, giving insight into the electronic origin of the absorption spectra.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not.The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. First-principles modeling of dye-sensitized solar cells: From the optical properties of standalone dyes to the charge separation at dye/TiO2 interfacesValentin Diez-Cabanes, Simona Fantacci, Mariachiara

Photochromic compounds are employed in implementing neuron surrogates. They will boost the development of neuromorphic engineering in wetware. In this work, the photochromic behaviours of (E)-3,4,6-trichloro-2-(p-diazenil)-phenol (t-DZH) and its conjugated phenoxide base (t-DZ) have been investigated experimentally in three different media: (1) pure acetonitrile, (2) in water and acetonitrile mixed in a 1/1 volume ratio, and (3) in an aqueous micellar solution of 3-(N,N-Dimethylmyristylammonio)propanesulfonate (SB3-14). The analysis of the spectral and kinetic features of t-DZH and t-DZ has been supported by quantum-mechanical DFT calculations, the maximum entropy method, and the determination of their colourability (C). The versatility of t-DZH and t-DZ makes them promising molecular probes of micro-environments and potential ingredients of photochemical oscillators required for implementing pacemaker neurons capable of communicating through optical signals in wetware.

The cooling mechanism of hot carriers (HC) in metal halide perovskites is a topic of debate which gathered huge attention due to its critical role in the performance of perovskite-based optoelectronics. HC cooling in 2D perovskites is faster than in its 3D counterpart, whereas in 2D/3D perovskites cooling becomes faster with decreasing the thickness of the inorganic quantum wells. Using state-of-the art first principles calculations it is showed that the modulation of electron-phonon (e-ph) coupling strength between bending and stretching phonon branches can explain this observation. Starting from the prototype BA(2)PbI(4) and PEA(2)PbI(4) 2D perovskites, e-ph coupling of individual phonon modes is investigated for 2D/3D perovskites with n = 1 and 3, along with a vis-& agrave;-vis comparison with the prototypical 3D MAPbI(3) system. This study shows that e-ph coupling with high-frequency stretching phonon modes in the 60-120 cm(-1) range is highest for n = 1 while it decreases with increasing the quantum well layers, by approaching the 3D bulk limit where e-ph coupling with low-frequency bending phonon modes (<60 cm(-1)) is dominant. Longer spacer cations with identical quantum well structures have a limited impact on the e-ph coupling, highlighting that the primary factor governing HC cooling is the quantum confinement within the inorganic sublattice. This study provides an advancement in the understanding of the mode-specific e-ph mediated HC cooling mechanism in metal-halide perovskites and can provide a route map toward tuning the e-ph interaction, which is instrumental for effectively gathering HC in solar cell devices.

Both historic and modern synthetic pigments and dyes used in painting are susceptible to alteration due to their interaction with light, atmospheric moisture, oxygen, and other agents of degradation of the environment and of the painting substrate. Unfortunately, a severe and irreversible alteration process is taking place in many artworks of invaluable relevance in Cultural Heritage. For this reason, art conservation has turned to fundamental science, where modern analytical and spectroscopic techniques could revolutionize our approach to the preservation and restoration of world heritage artworks. Among the state-of-the-art experimental techniques, photoluminescence plays a central role, both to evidence the constituting materials and to individuate the degradation process based on the variations with respect to a pristine material. Theoretical simulations, which have been proven highly successful in the modeling, design, and characterization of materials is proposed as a “clean” and not invasive technique that can complement the experimental investigation in disclosing information on materials employed in works of art. The present chapter aims to emphasize the contribution of theoretical modeling to photoluminescence analysis on colorants in degraded artworks and to highlight its effectiveness in the interpretation of experimental measurements. We focus on both pigments and dyes that present completely different structural and electronic properties require different methodological approaches. In the chapter, a critical overview of the theoretical methods used to describe the luminescence of dyes and pigments is presented along with a discussion of the case studies of both classes of colorants present in the scientific literature.

Computational modelling applied to cultural heritage can assist the characterization of painting materials and help to understand their intrinsic and external degradation processes. The degradation of the widely employed zinc oxide (ZnO)—a white pigment mostly used in oil paints—leads to the formation of metal soaps, complexes of Zn ions and long-chain fatty acids coming from the degradation of the oil binder. Being a serious problem affecting the appearance and the structural integrity of many oil paintings, it is relevant to characterize the structure of these complexes and to understand the reaction pathways associated with this degradation process. Density functional theory (DFT) calculations were performed to investigate the adsorption of the acetate and acetic acid on relatively large ZnO clusters and the formation of Zn–acetate complexes. Carboxylic acids with longer alkyl chains were then investigated as more realistic models of the fatty acids present in the oil medium. In addition, DFT calculations using a periodic ZnO slab were performed in order to compare the obtained results at different levels of theory. Optimization calculations as well as the formation energies of the ZnO@carboxylate coupled systems and the thermodynamics leading to possible degradation products were computed. Our results highlight the potential for DFT calculations to provide a better understanding of oil paint degradation, with the aim of contributing to the development of strengthening and conservation strategies of paintings.

In this study, oxidative degradation of dyes Orange G (OG) and Eosin Y (EY) by TiO 2 as catalyst was explored in air-equilibrated aqueous dispersions under UV light irradiation. To determine the optimal operating conditions for degradation, various effects were investigated, such as pH of dye dispersion, addition of cationic surfactants and specific additive. The photodegradation efficiency of both dyes was significantly enhanced at alkaline pH, particularly in the presence of tetraalkylammonium bromide surfactants, as they promote the mutual interaction between dye and TiO 2 surface, otherwise prevented due to their negative charge in basic condition. Surfactant concentration also played an important role, because it influences the state of surfactant aggregation on the semiconductor surface. The kinetic trend of the fragmentation process was strongly affected by different hydrophobic and electrostatic interactions that OG and EY and their derivative intermediates are able to establish with surfactant/TiO 2 in various forms of aggregation, as well as by their redox properties. Density functional theory (DFT) calculations of charge distribution and Gibbs free energy changes of solvation, performed on optimized molecular geometry, were useful to support and rationalize the surfactant involvement on the degradation process.

The synergistic catalytic effect of surfactants is highlighted in the photodegradation of Orange G and Eosin Y by TiO2 at alkaline pH.

Titanium dioxide (TiO 2 ) has been used in numerous paintings since its creation in the early 1920s. However, due to this relatively recent adoption by the art world, we have limited knowledge about the nature and risk of degradation in museum environments. This study expands on the existing understanding of TiO 2 facilitated degradation of linseed oil, by examining the effect of visible light and crystallographic phase (either anatase or rutile) on the reactivity of TiO 2 . The present approach is based on a combination of experimental chemical characterization with computational calculation through Density Functional Theory (DFT) modeling of the TiO 2 -oil system. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FT-IR) enabled the identification of characteristic degradation products during UV and visible light aging of both rutile and anatase based paints in comparison to BaSO 4 and linseed oil controls. In addition, cratering and cracking of the paint surface in TiO 2 based paints, aged under visible and UV–vis illumination, were observed through Scanning Electron Microscopy (SEM). Finally, Density Functional Theory (DFT) modeling of interactions between anatase TiO 2 and oleic acid, a fatty acid component of linseed oil, to form a charge transfer complex explains one possible mechanism for the visible light activity observed in artificial aging. Visible light excitation of this complex sensitizes TiO 2 by injecting an electron into the conduction band of TiO 2 to generate reactive oxygen species and subsequent degradation of the oil binder by various mechanisms (e.g., formation of an oleic acid cation radical and other oxidation products). Graphical Abstract

The role of tetraalkylammonium bromide surfactants on the TiO2 photocatalyzed degradation of Alizarin, Purpurin and Bromothymol Blue has been studied in air-equilibrated aqueous medium under UV light irradiation. Alizarin has also been investigated by carrying out the photodegradation in TiO2/surfactant dispersions irradiated by natural solar light. Absorption spectral analysis showed that the photodegradation efficiency of the dyes was significantly enhanced by the addition of the cationic surfactants. The effect of pre-micellar, micellar and post-micellar concentrations of the surfactants was analyzed to gain insight into the mechanism of the surfactant-assisted TiO2-photocatalytic degradation of the three dyes. The findings revealed that various parameters, such as initial pH, dye pK's, type of water and light source exerted their influence on the photocatalytic degradation. The results were explained on the basis of hydrophobic and electrostatic interactions between dye and surfactant/TiO2 in the various forms of aggregation. Density functional theory (DFT) calculations of charge distribution and Gibbs free energy changes of solvation of the species involved were used as a support in rationalizing the surfactant effect on the photodegradation process.

Whereas there is an increasing amount of reports on the second-order nonlinear optical (NLO) and luminescence properties of tetradentate [N2O2] Schiff base–zinc complexes, the study of zinc complexes having two bidentate [NO] Schiff-base ligands is relatively unexplored from an NLO point of view. This work puts in evidence that the known chiral bis{2-[(R)-(+)-1-phenylethyliminomethyl]phenolato-N,O}zinc(II) complex is a fascinating multifunctional molecular inorganic–organic hybrid material characterized by interesting second-order NLO and luminescent properties in solution. The emissive properties of the organic 2-(R)-(+)-1-phenylethyliminomethyl]phenol proligand are greatly enhanced upon coordination to the inorganic Zn(II) center.

A novel highly luminescent N^C^N Pt(ii) complex with a thiolate ligand allows fabrication of efficient processable solution-OLEDs with a tuneable color.