54 research outputs found
High Second-Order NLO Response Exhibited by the First Example of Polymeric Film Incorporating a Diimine-Dithiolate Square-Planar Complex: The [Ni(o-phen)(bdt)]
No full textA novel square-planar diimine-dithiolate nonlinear optical (NLO) chromophore, the complex [Ni(o-phen)(bdt)] (1), is reported in this paper (o-phen = dianion of 1,2-phenylendiamina; bdt =1,2-benzenedithiolate). This compound has been fully characterized by single-crystal X-ray diffraction, UV-vis-NIR spectroscopy, cyclic voltammetry, DFT, and TD-DFT calculations. 1 crystallizes in the P21 space group and shows an almost planar molecule. The cyclic voltammetry measurements present an irreversible anodic peak at 0.87 V and reversible and quasi-reversible reduction waves at -0.35 and -1.13 V, respectively. A medium-intense (ε = 1.91 × 104 mol-1 dm3 cm-1) absorption with a maximum at 728 nm appears in the UV-vis-NIR spectrum. The molecular second-order NLO properties of 1 have been measured by the electric field induced second-harmonic generation technique in DMF solution, giving values of -1000 × 10-48 esu for μβ1.907 and -356 × 10-48 esu for μβ0. Furthermore, remarkable solid-state responses have been measured for polymeric films of 1. Indeed, this complex has been embedded into poly(methyl methacrylate) poled films showing high NLO response (d33 = 1.90 ± 0.38 pm/V), higher than those previously reported for similar push-pull metal complexes. Moreover, 1 represents the first example of a diimine-dithiolate chromophore incorporated into a NLO-active film
Nonlinear-Optical Properties of α-Diiminedithiolatonickel(II) Complexes Enhanced by Electron-Withdrawing Carboxyl Groups
No full textWe report the synthesis, characterization, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations for three nickel diiminedithiolate complexes [Ni(4,4′-R2carboxy-bpy)(L)] [R = methyl, L = 1,2-benzenedithiolate (bdt), 1; R = ethyl, L = 5,6-dihydro-1,4-dithine-2,3-dithiolate (dddt), 2; R = ethyl, L = 1-(N-methylindol-5-yl)ethene-1,2-dithiolate (mi-5edt), 3]. The crystal structure of 1 shows a square-planar coordination for the nickel ion and bond distances consistent with a diiminedithiolate description for the complex. For all complexes, the cyclic voltammetry measurements show two reversible reduction processes (−1.353/–1.380 V and −0798/–0.830 V, respectively) and an anodic wave (+0.372/+0.601 V). The UV–vis spectra present a band around 600–700 nm (ε = 4880–6000 dm3 mol–1 cm–1) mainly attributed to a charge-transfer highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition, which shows a large negative solvatochromic shift, characteristic of push–pull complexes, and is responsible for the NLO properties of these molecules. The charge-transfer character of this electronic transition is confirmed by DFT calculations, with the HOMO mainly centered on the dithiolate moiety and the LUMO on the bpy ligand, with important contribution given by the carboxyl groups (≈13%). Small contributions from the nickel(II) ion are present in both of the frontier orbitals. The carboxyl groups enhance the optical properties of this class of complexes, confirmed by comparison with the corresponding unsubstituted compounds. The second-order NLO properties have been measured by an electric-field-induced second-harmonic-generation technique using a 10–3 M solution in N,N-dimethylformamide and working with a 1.907 μm incident wavelength, giving for μβ1.907 (μβ0) values of −1095 (−581), −2760 (−954), and −1650 (−618) × 10–48 esu for 1–3, respectively. These values are among the highest in the class of square-planar push–pull complexes, similar to those found for dithionedithiolate compounds. Moreover, spectroelectrochemical experiments demonstrate the possibility of using these complexes as redox-switchable NLO chromophores
Tuning the LUMO energy of 1,10-phenanthroline in ??-diimine???dithiolate Ni(II) complex and enhancement of nonlinear optical properties
No full textThe synthesis, characterization, nonlinear optical properties and DFT calculations for a new Ni-diiminedithiolate complex [Ni(Cl4-phen)(mi-5edt)] (Cl4-phen = 3,4,7,8-tetrachloro-1,10-phenanthroline; mi-5edt = 1-(N-methylindol-5-yl)-ethene-1,2-dithiolate), are reported. The UV–Vis spectrum shows a solvatochromic absorption at 700 nm in DMF (ε = 5520 mol−1 dm3 cm−1) due to a charge-transfer (CT) highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition, typical of push–pull complexes. The CT character of this electronic transition is confirmed by DFT calculations with the HOMO mainly centered on the mi-5edt moiety and the LUMO on the Cl4-phen ligand. By comparison with the unsubstituted analogue compound, computational studies confirm the role of the chlorination enhancing the optical properties of this complex. The second order nonlinear optical properties were measured by EFISH technique (at 1.907 μm), giving values of −2030 and −810 × 10−48 esu for μβ1.907 and μβ0, respectively. These values are among the highest reported so far for the class of d8 square-planar push–pull compounds.<br/
beta-substituted ZnII porphyrins as dyes for DSSC: a possible approach to photovoltaic windows
No full textThe development of building integrated photovoltaic (BIPV) technology and its implementation in construction of the building envelop provide aesthetical, economical and technical solutions toward the zero-energy building. In this perspective dye-sensitized solar cells (DSSCs), which can be obtained in transparent form and with tunable different colors, offer not only an alternative to the traditional silicon solar cells to be applied in particular to decorative effects on windows and glass integrated facades, but also to indoor structures (and furnishings) in order to recapture the energy spent for the inner lighting, thanks to their peculiar ability of operating in diffuse light condition. In this context, porphyrin-based molecules have an immense potential as light harvesting component of dye-sensitized nanocrystalline TiO2 solar cells, reaching now efficiencies up to about 13%. However the multistep synthesis of the best performing porphyrin dyes, showing a meso substitution pattern, is characterized by very low overall yields compromising their possible applicative development for instance in large photovoltaic (PV) glass modules in competition with the actual commercial PV glass modules based on CuInGaSe2 or CdTe thin voltaic films. In this review the renewed interest in the role of the beta-substituted Zn-II porphyrins for PV application, less studied than the mesa substituted ones, is highlighted. Indeed they can rely on a more accessible synthetic procedure since their tetraaryl porphyrinic core can be easily obtained by a one pot reaction between pyrrole and the appropriate aryl aldehyde. Moreover, their remarkable light harvesting properties in the visible range as well as their peculiar steric hindrance, which strongly opposes to the charge recombination process at the photoanode/dye/electrolyte interface, make this kind of cost-effective porphyrinic dyes more promising for application in new PV glass modules based on DSSC technology, to be applied BIPV
Porphyrins for second order nonlinear optics (NLO) : an intruguing history
No full textThis short review outlines the main results obtained by our research group over the last 15 years in the field of porphyrins and metal porphyrins for second order nonlinear optics (NLO). This overview aims to provide a general framework of the key factors which affect the second order NLO response of porphyrin chromophores. The pivotal role of the porphyrin ring as π-conjugated linker, the nature of the metal center, the substitution pattern which features the geometrical arrangement of donor and acceptor substituents in the different classes of porphyrin NLO-phores, as well as the aggregation phenomena and the role of solvents are addressed in detail
Efficient sunlight harvesting by A4 b-pyrrolic substituted ZnII porphyrins : a mini-review
No full textDye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived π* singlet excited states. Moreover, the presence of four meso and eight β-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans-A2BC push-pull ZnII porphyrins, characterized by a strong and directional electron excitation process along the push-pull system, have been extensively investigated. On the other hand, A4 β-pyrrolic substituted tetraaryl ZnII porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A4 β-substituted ZnII porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso-substituted analogs
Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials
No full textIn this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and Zn-II complex), carrying in 2 or 2,12 beta-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of mu beta(1907). Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to gamma(EFISH) of the purely electronic cubic term gamma(-2 omega; omega, omega, 0), which prevails on the quadratic dipolar orientational one mu beta(-2 omega; omega, omega)/5kT, as confirmed by computational evidence
Comparison of the Skeletal and Dento-Alveolar Changes Obtained with a Customized Elastodontic Appliance and Twin Block: A Prospective Investigation
No full textObjectives: This study aimed to compare the skeletal and dentoalveolar effects of a fully customized elastodontic appliance with those of the traditional Twin Block appliance in growing patients with Class II malocclusion during the mixed dentition phase. Methods: A total of 35 patients were included: 18 treated with a customized elastodontic appliance (C-Ela group) and 17 with a Twin Block appliance (TB group). Digital dental models and lateral cephalometric radiographs were obtained at baseline (T1) and after 12 months of treatment (T2). All patients were treated by experienced clinicians according to standard-ized appliance protocols. Data analysis was performed by a blinded operator using Ortho Analyzer and Dolphin Imaging software. The Shapiro–Wilk test was applied to verify the normal distribution of the data. Paired-sample t-tests were used to assess within-group changes between T1 and T2. For intergroup comparisons two-tail independent-sample t-tests were used, and chi-square tests were used for categorical variables. Statistical signif-icance was set at p < 0.05. Results: Both groups showed significant intragroup improve-ments in overjet (C-Ela: −2.77 ± 2.07; TB: −2.30 ± 2.72 mm), overbite (C-Ela: −1.79 ± 1.95; TB: −1.40 ± 2.65 mm), and sagittal molar relationship (p < 0.05) after treatment. The C-Ela group exhibited a significantly greater reduction in anterior dental crowding (p < 0.05) and better control of upper (C-Ela: −4.93 ± 7.65°; TB: −1.80 ± 5.72°) and lower incisor incli-nation (C-Ela: +1.70 ± 4.80°; TB: +4.35 ± 6.22°). In intergroup comparisons, the TB group showed a significantly greater proclination of the lower incisors at T2 (L1/Go-Gn: +4.35°; L1/A-Pog: +1.44 mm), whereas the C-Ela more effectively limited these changes (L1/Go-Gn: +1.70°; L1/A-Pog: +1.18 mm). Skeletal analysis revealed an increase in ANB angle in both groups (C-Ela: −1.49 ± 2.62°; TB: −1.78 ± 2.78°), with no statistically significant inter-group differences, and no other skeletal parameters showed significant between-group changes. Conclusions: Both appliances effectively corrected Class II malocclusions. How-ever, the customized elastodontic device provided better dentoalveolar control, particu-larly in managing anterior crowding and incisor inclination. Its individualized fit may enhance biomechanical precision and improve overall treatment outcomes in growing pa-tients
Effect of torsional twist on 2nd order non-linear optical activity of anthracene and pyrene tricyanofuran derivatives
No full textTricyanofuran (TCF) derivatives attached to both anthracene and pyrene moieties were synthesised and characterised by optical, electrochemical and computational techniques. Both compounds exhibited similar absorption profile as well as electrochemical behaviour, however the pyrene derivative showed 20-fold higher non-linear optical activity measured by the EFISH technique. This huge difference has been assigned to (i) a lower molar absorption and (ii) a higher torsion angle for the anthracene derivative, confirmed by both experimental X-ray diffraction and DFT calculations. Furthermore, we note that the μβ1.907 value of −1700 × 10−48 esu recorded for the pyrene derivative in CHCl3/pyridine is remarkable for a NLO chromophore lacking a classical push–pull structure
Capping agent effect on Pd-supported nanoparticles in the hydrogenation of furfural
No full textThe catalytic performance of a series of 1 wt % Pd/C catalysts prepared by the sol-immobilization method has been studied in the liquid-phase hydrogenation of furfural. The temperature range studied was 25–75 °C, keeping the H2 pressure constant at 5 bar. The effect of the catalyst preparation using different capping agents containing oxygen or nitrogen groups was assessed. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and poly (diallyldimethylammonium chloride) (PDDA) were chosen. The catalysts were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization data suggest that the different capping agents affected the initial activity of the catalysts by adjusting the available Pd surface sites, without producing a significant change in the Pd particle size. The different activity of the three catalysts followed the trend: PdPVA/C > PdPDDA/C > PdPVP/C. In terms of selectivity to furfuryl alcohol, the opposite trend has been observed: PdPVP/C > PdPDDA/C > PdPVA/C. The different reactivity has been ascribed to the different shielding effect of the three ligands used; they influence the adsorption of the reactant on Pd active sites
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