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The stratum corneum (SC) plays an important role in skin barrier function. It acts as a protective barrier against water loss, eliminates foreign substances and micro-organisms and acts against harmful effects of UVR.Our aim was to study the impact of suberythemal doses of UVA and UVB exposure on the molecular structure, organization and barrier function of the SC by following different Raman descriptors.Twenty female volunteers, aged 20-30 years, with healthy skin were enrolled. Doses of 95 mJ/cm² UVA and 15 mJ/cm² UVB were applied to volunteers’ forearms. In vivo Raman measurements were performed at irradiated and control regions.The impact of UVA and UVB irradiation was observed following several Raman descriptors, i.e. the ratio of vasymCH2/vsymCH2 (2885 cm-1/2850 cm-1) corresponding to the organizational order of the lipid bilayer. Water content and mobility descriptors were obtained by calculating vOH/vCH ratio. Finally, protein secondary structure was evaluated based on the 1670 cm-1/1650 cm-1 ratio related to β sheets and α helices, respectively.UVA induced a loosening of the lateral packing of lipids immediately after irradiation. In contrast, delayed impact caused a tightening of the lipid barrier, an increase in water content -mainly in the unbound water fraction and a higher relative amount of β sheets in SC proteins. Overall, these observations may explain the thickening of the SC observed in previous studies. A UVB dose of 15 mJ/cm² was apparently below the threshold necessary to induce significant changes despite the trends observed in this study.

The stratum corneum (SC) plays an important role in skin barrier function. It acts as a protective barrier against water loss, eliminates foreign substances and micro-organisms and acts against harmful effects of UVR. our aim was to study the impact of suberythemal doses of UV

Our work on new chemiluminescent substances related to the marine luciferin coelenterazine (λmax = 465 nm) led us to attempt the synthesis of four nitrogen-rich pyridopyrazine-bearing analogues. Accordingly, the preparation of the corresponding benzyl-bearing pyridopyrazinols is studied. By varying the conditions for the condensation of phenylpyruvic acid with 1,2-diaminopyridine or 3,4-diaminopyridine, all the possible pyridopyrazin-2-ol regioisomers are isolated and properly characterized, including by means of crystallographic studies. The ensuing syntheses of the halogenated pyridopyrazines are fraught with difficulties ranging from extensive decomposition to an unexpected ring contraction. In one instance, the inherently reductive mixture of phosphorus oxychloride and phosphorus trichloride provides 2-benzyl-3-chloropyrido[2,3-b]pyrazine. This precursor is then transformed into the target O-acetylated luciferin (6,8-dibenzylimidazo[1,2-a]pyrido[3,2-e]pyrazin-9-yl acetate). The ‘benzo’ derivative of this analogue (i.e., 2,12-dibenzylimidazo[1′,2′:1,6]pyrazino[2,3-c]isoquinolin-3-yl acetate) is also prepared and the chemiluminescence emission spectra of these compounds are determined in a phosphate buffer (λmax = 546 and 462 nm).

International audience; In our work on the design and studies of luciferins related to the blue‐hued coelenterazine, we undertook the synthesis of heterocyclic analogues susceptible to produce a photon, possibly at a different wavelength. We describe here the synthesis of O‐acetylated derivatives of imidazo[1,2‐b]pyridazin‐3(5H)‐one, imidazo[2,1‐f][1,2,4]triazin‐7(1H)‐one, imidazo[1,2‐a]pyridin‐3‐ol, imidazo[1,2‐a]quinoxalin‐1(5H)‐one, benzo[f]imidazo[1,2‐a]quinoxalin‐3(11H)‐one, imidazo[1',2':1,6]pyrazino[2,3‐c]quinolin‐3(11H)‐one and 5,11‐dihydro‐3H‐chromeno[4,3‐e]imidazo[1,2‐a]pyrazin‐3‐one thanks to an extensive use of the Buchwald‐Hartwig N‐arylation. The acidic hydrolysis of these derivatives then gave solutions of the corresponding luciferin analogues which we studied. Not too unexpectedly, even if these were “dressed” with substituents found in actual substrates of the nanoKAZ/NanoLuc luciferase, no bioluminescence was observed with these compounds. However, in a phosphate buffer, all produced a light signal, by chemiluminescence, with extensive variations in their respective intensity and this could be increased by adding a quaternary ammonium salt in the buffer. This aspect was actually instrumental to determine the emission spectra of many of these luciferin analogs.

An important aspect of the biomechanical behaviour of the stratum corneum (SC) is the drying stresses that develop with water loss. These stresses act as a driving force for damage in the form of chapping and cracking. Betasitosterol is a plant sterol with a structure similar to cholesterol, a key component in the intercellular lipids of the outermost layer of human skin, the SC. Cholesterol plays an important role in stabilizing the SC lipid structure, and altered levels of cholesterol have been linked with SC barrier abnormalities. Betasitosterol is currently applied topically to skin for treatment of wounds and burns. However, it is unknown what effect betasitosterol has on the biomechanical barrier function of skin. Here, by analysing the drying stress profile of SC generated during a kinetics of dehydration, we show that betasitosterol, in combination with two emollient molecules, isocetyl stearoyl stearate (ISS) and glyceryl tri-2-ethylhexanoate (GTEH), causes a significant modulation of the drying stress behaviour of the SC by reducing both the maximal peak stress height and average plateau of the drying stress profile. Raman spectra analyses demonstrate that the combination of betasitosterol with the two emollients, ISS and GTEH, allows a high water retention capacity within the SC, while the lipid conformational order by increasing the amount of trans conformers. Our study highlights the advantage of combining a biomechanical approach together with Raman spectroscopy in engineering a suitable combination of molecules for alleviating dryness and dry skin damage.

A dodecapeptide (AMRKLPDAPGMH) functionalized with a tetramethylrhodamine (TAMRA) chromophore at the N-terminus was immobilized on nanocrystalline TiO2. The optical and binding properties of the peptide layer immobilized on the titania surface were characterized by UV–vis absorption, steady-state fluorescence and X-ray photoelectron spectroscopies. Circular Dichroism experiments and Molecular Mechanics calculations showed that the predominant conformation populated by the peptide scaffold brings Arg3, Lys4 and Asp7 in the correct position for linking the TiO2 surface. Photocurrent generation experiments were therefore carried out to determine the photon-to-current conversion efficiency (IPCE) of a Grätzel-like Dye Sensitized Solar Cell (DSSC), the photoactive unit of which is formed by TAMRA-AMRKLPDAPGMH/TiO2. The measured IPCE amounted to 0.65%, a value that is definitely low, but superior to those previously reported for similar bioinspired DSSCs. This result can be ascribed to the light-harvesting properties of the TAMRA chromophore and to the unique structural properties of the peptide spacer. © 2017 Elsevier B.V.

Three new copper(I) complexes [Cu(LX)2]+(PF6-) (where LX stands for 2,9-dihalo-1,10-phenanthroline and X = Cl, Br, and I) have been synthesized in order to study the impact of halogen substituents tethered in the α position of the chelating nitrogen atoms on their physical properties. The photophysical properties of these new complexes (hereafter named Cu-X) were characterized in both their ground and excited states. Femtosecond ultrafast spectroscopy revealed that early photoinduced processes are faster for Cu-I than for Cu-Cl or Cu-Br, both showing similar behaviors. Their electronic absorption and electrochemical properties are comparable to benchmark [Cu(dmp)2]+ (where dmp stands for 2,9-dimethyl-1,10-phenanthroline); furthermore, their optical features were fully reproduced by time-dependent density functional theory and ab initio molecular dynamics calculations. All three complexes are luminescent at room temperature, showing that halogen atoms bound to positions 2 and 9 of phenanthroline are sufficiently bulky to prevent strong interactions between the excited Cu complexes and solvent molecules in the coordination sphere. Their behavior in the excited state, more specifically the extent of the photoluminescence efficiency and its dependence on the temperature, is, however, strongly dependent on the nature of the halogen. A combination of ultrafast transient absorption spectroscopy, temperature-dependent steady-state fluorescence spectroscopy, and computational chemistry allows one to gain a deeper understanding of the behavior of all three complexes in their excited state.

This study aims to explore the spectroscopic properties of a Sr1.0Ba2.0B6O12:0.5Sm3+ phosphor synthesized using the solid-state reaction method. The morphology and elemental composition of the phosphor were determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. Phase changes and crystallite phases in the phosphor were studied using differential-scanning calorimetry and X-ray diffraction, respectively. Raman and Fourier-transform infrared spectra were used to identify the molecular vibrations in the phosphor. The energy bandgap and bonding nature of the phosphor were analyzed using the absorption spectrum. The nephelauxetic ratios determined from the absorption peaks revealed the presence of both ionic and covalent bonding in the phosphor. Judd-Ofelt parameters, along with radiative properties of the phosphor, were evaluated using the peaks in the absorption spectrum. Colorimetric analysis using the photoluminescence spectrum showed that the Sr1.0Ba2.0B6O12:0.5Sm3+ phosphor emits a cool-white light. The higher values of the spectroscopic quality factor, stimulated-emission cross-section, quantum efficiency, and the white-light emission of the phosphor suggest that Sr1.0Ba2.0B6O12:0.5Sm3+ is useful for display and lighting applications.

Background: In vivo Raman spectroscopy is a powerful tool for real-time analysis and in situ evaluation of tissues such as the skin. The efficiency of this technique has been widely demonstrated as a label-free method for in vivo evaluation of the skin. The aim of this study is to gather information about inter- and intra-individual variations in the spectral descriptors of water content and structure, organization of the lipid barrier and structure of proteins in the stratum corneum (SC). Methods: In vivo SC measurements were performed on 17 female volunteers aged 20-30 years (phototypes I and II). For intra-individual variability, spectral collection was performed on 5 successive days per volunteer. Shapiro-Wilk and Cochran tests were applied to check the normality and the homoscedasticity of variances. ANOVA was then applied to evaluate intra- and intergroup variability. Results: ANOVA was performed on the spectral descriptors of water content and structure, organization of the lipid barrier and secondary structure of proteins in the SC. No significant intra- and interday variability was observed for all volunteers. Despite the low value of the total relative standard deviation, a highly significant variation was observed between volunteers. Conclusion: Interindividual variability for Raman measurements is significant for a set of volunteers with normal nondiseased SC and close phototypes. This variability should be taken into consideration as a threshold for significant variance when working in vivo.

We investigate the new simultaneous absorbance-transmission and fluorescence excitation-emission matrix method for rapid and effective characterization of the varying components from a mixture. The absorbance-transmission and fluorescence excitation-emission matrix method uniquely facilitates correction of fluorescence inner-filter effects to yield quantitative fluorescence spectral information that is largely independent of component concentration. This is significant because it allows one to effectively monitor quantitative component changes using multivariate methods and to generate and evaluate spectral libraries. We present the use of this novel instrument in different fields: i.e. tracking changes in complex mixtures including natural water, wine as well as monitoring stability and aggregation of hormones for biotherapeutics.

While copper(I)-bis(diimine) complexes [Cu-I(L)(2)](+) are considered as potent substitutes for [Ru-II(bpy)(3)](2+), they exhibit low molar extinction coefficients with respect to ruthenium parent analogues. One interesting possibility to improve the light collection ability of [Cu-I(L)(2)](+) consists in increasing the length of the Cu-L dipole. In order to achieve this goal, we propose in this contribution to fuse aromatic rings onto the 2,9-di-nbutyl-1,10-phenanthroline core and examine how the properties of the corresponding copper(I) complexes are impacted. Electrochemical, absorption and emission properties are assessed; rewardingly, the envisioned approach was successful since extinction coefficients above 10,000 M-1.cm(-1) were measured. All copper(I) complexes remain photoluminescent, with emission maxima greatly varying from 725 to 815 nm, strongly affected by the molecular structures. A rationale to explain the variations of the emission quantum yields is proposed. (C) 2017 Elsevier Ltd. All rights reserved.

Methacrylate polymers containing different molar contents of nonlinear optical (NLO) active molecular segments based on 2-[4-(N-methyl,N-hydroxyethyl-amino)phenylazo]-phenyl-6-nitrobenzoxazole chromophores were synthesized, and their phase behavior and second-order NLO properties were investigated. Polymers containing 6 –17 mol % chromophore segments allowed the preparation of amorphous and optically clear thin films. Some mesomorphic structuration was exhibited by a polymer with 33 mol % chromophoric units. However, this feature did not prevent the possibility of investigating the NLO properties. Nonlinear resonance-enhanced d33 coefficients were determined by second harmonic generation experiments on spin-coated, corona-poled thin films at lambda= 1064 nm. Values ranging from 40 to 60 pm/V were measured with increasing chromophore molar contents.

We investigate the new simultaneous absorbance-transmission and fluorescence excitation-emission matrix method for rapid and effective characterization of the varying components from a mixture. The absorbance-transmission and fluorescence excitation-emission matrix method uniquely facilitates correction of fluorescence inner-filter effects to yield quantitative fluorescence spectral information that is largely independent of component concentration. This is significant because it allows one to effectively monitor quantitative component changes using multivariate methods and to generate and evaluate spectral libraries. We present the use of this novel instrument in different fields: i.e. tracking changes in complex mixtures including natural water, wine as well as monitoring stability and aggregation of hormones for biotherapeutics.

Polymethacrylate and polycondensated polymers based on chromophores containing the s-triazolo[3,4-b]-thiadiazole heterocycle were synthesized. Chromophore and polymer preparations are described. Second order NLO measurements are reported for polymers and for one functionalized chromophore. The maximum value of second harmonic generation coefficient (d(33)) measured is 11.5 pm/V at incident laser wavelength of 1368 nm. For the most active polymer, 85% of the initial d(33) value is retained after 27 days at 80 degrees C.

New polyurethanes containing Y-shaped chromophores, symmetrical derivatives of 4-(dicyanomethylene)-2-methyl-6- [p- (dimethylamino)styryl]-4H-pyran, have been prepared. The polymers show high glass transition temperatures (Tg) and a good thermal stability. SHG measurements on poled polymer films of the synthesized polymers have been carried out and a maximum d 33 of 15 pm·v -1 has been found at 1368 nm fundamental wavelength. Time stability measurements on the most active polymer have shown that after the initial fast relaxation, the d 33 value remains constant at 80 °C for 60 d.

The orientation relaxation of azo-dyes upon all-optical poling was studied. Azo-dye doped amorphous polymers were poled for different durations by all-optical poling at several temperatures. A quasi-permanent macroscopic second-order nonlinear optical susceptibility χ(2) was inscribed in the dye-doped centrosymmetric polymer systems. Relaxation of the χ(2) was monitored by second harmonic generation. It shows that the polar orientation relaxation follows the duration of the poling process: the longer the poling, the slower the polar relaxation time. Causes of the orientation relaxation retardation are discussed.

We report on the fluorescence efficiency of four infrared (IR) polymethine dyes. These figures have been determined using an indirect method based on a fluorescence standard (Rhodamine B in ethanol). The fluorescence decay times have been measured too and their correlation with the quantum efficiency data has been shown. The optical behavior of the IR dyes in three solvents with different polarities has been compared and discussed.

In the present work we report on steady-state and dynamical optical properties of four polymethine dye molecules absorbing in the near infrared (IR) region (0.8–1.1 μm) and emitting around 1.2 μm. The molecules are embedded in organically modified silicate (ORMOSIL) material synthesized by a sol-gel method. The investigated samples were prepared as films, deposited on glass substrates. Steady-state absorption and emission measurements have been accomplished for the chromophores in solution as well as in hybrid organic/inorganic films in order to determine the effect of the solid cage on the optical properties of the chromophore. To better understand the influence of the solid network, we also measured for some of the investigated molecules emission transients with femtosecond time resolution. An estimation of the emission quantum yield of the IR dye molecules in a glassy matrix is also given. The kinetic results are sensitive to guest-host interactions.

A bioinspired approach is applied to photoelectric conversion devices. A 3(10)-helical hexapeptide bearing a pyrene unit is immobilized on a gold-covered TiO2 surface. The device is integrated for the first time in a dye-sensitized solar cell, exhibiting stability after several measurements. The approach could have promising applications in the field of optoelectronics.

Azobenzene-substituted polythiophenes were prepared by copolymerization of 3-alkylthiophenes functionalized with an azo-chromophore and 3-alkylthiophenes as plastifying comonomers to improve solubility. Monomers with different oligomethylenic spacer and alkylic chain lengths were synthesized and copolymerized via FeCl3 oxidative polymerization. Polymer soluble fractions were characterized by 1H and 13C NMR, FTIR, UV–Vis spectroscopy, and GPC, DSC and TGA. Second-order non-linear optical properties were measured by the second harmonic generation technique.

We show that SiGe islands are transformed into nanoholes and rings solely by annealing treatments and without Si capping. Rings are produced by a rapid flash heating at temperatures higher than the melting point of Ge, whereas nanoholes are produced by several minutes of annealing. The rings are markedly rich in Si with respect to the pristine islands, suggesting that the evolution path from islands to rings is driven by the selective dissolution of Ge occurring at high temperatures. © 2013 Elsevier B.V. All rights reserved.

In this work, the effect of reverse bias stress tests on Dye Solar Cells (DSCs) based on N719 dye was investigated in detail using resonant micro-Raman spectroscopy. First the Raman lines were assigned to vibrations from the different constituents in a fresh solar cell. Then the mechanism of thiocyanato (SCN − ) loss under stress conditions was reported.

We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second-order NLO characterization has been performed. An out-of-resonance d33 coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007

Two NLO azo-benzimidazolic chromophores, bis-ethanol, 2,2′-[[4-[[4-(1-ethyl-6-nitro-1H-benzimidazol-2-yl)phenyl]azo]phenyl]imino] (BZI1) and bis-ethanol, 2,2′-[[4-[[4-[(1E)-2-(1-ethyl-6-nitro-1H-benzimidazol-2-yl)ethenyl]phenyl]azo]phenyl]imino] (BZI2), properly functionalised for polycondensation reactions, have been used for the synthesis of new NLO polyurethanes and polyesters. The polymers have high thermal stability and T g ranging between 146 and 173 °C. Thin films of polymers have been prepared and oriented by electrical poling. The resonance free NLO activity has been measured at a fundamental wavelength of 1368 nm by second harmonic generation (SHG) and a maximum d 33 of 2.3 pm/V has been observed. Polymers containing the less active chromophore (BZI1, μβ = 950 × 10 −48 esu) show higher d 33 value than the analogous polymers containing BZI2 chromophore ( μβ = 1400 × 10 −48 ). A theoretical analysis suggests that this unexpected behaviour can be only partially attributed to thermodynamic effects, dynamical effects should also play a role.

Guest-host polymer system with potential use in electro-optic devices is discussed. The polymer host is a polyimide and the guest chromophore is Disperse Red 19 (DR 19). Decay times of poled order after corona poling procedure have been derived from the behaviour at elevated temperatures below glass transition temperature Tg using Arrhenius plots. An extrapolated lifetime greater than 30 years at room temperature has been obtained.

In this work we report on the preliminary results of compatibility, fabrication and characterization of two planar polymeric multilayer structures for electro-optic applications. The structures are composed by three polymeric layers grown on glass substrate. Buffer and cladding layers were synthesized using polymethylmethacrylate (PMMA). The guiding layers were composed by Polysulfone (PSU) and by a mixture of PMMA and polycarbonate (PC) both doped with Disperse Red 1 (DR1) molecules as nonlinear active units. Linear and nonlinear optical characterization of the structures by refractive index, absorption, optical losses, Second Harmonic Generation (SHG) and time stability measurements have been carried out.

Hybrid organic-inorganic materials doped with zwitterionic push-pull chromophores with high hyperpolarizability have been synthesized via sol-gel, based on glycidoxypropyltrimethoxysilane (GPTMS) and glycidoxypropylmethyldimethoxysilane (GDMMS). Homogeneous films doped with chromophores, have been obtained using N-hydroxyethylcarbazole as a physical spacer avoiding dye aggregation. Spin-coated doped films have been electrically poled in N2 atmosphere and second harmonic generation measurements have been performed in situ to confirm the nonlinear (NL) properties achieved after poling. The waveguiding properties of the films have been preliminarly measured by m-line spectroscopy before and after poling and the feasibility of channel waveguiding structures explored.

Summary: Two series of methacrylate copolymers were prepared, based on two new nonlinear optically (NLO) active chromophores 2-[4-(N-methacryloyloxyethyl-N-methylamino) phenylazo]-4,5-dicyanoimidazole (chromophore A) and 1-ethyl-2-[4-(N-methacryloyloxyethyl-N-methylamino)phenylazo]- 4,5-dicyanoimidazole (chromophore B). Second order NLO properties of the two series of copolymers (A or B as monomer and methyl methacrylate as the comonomer) were investigated by SHG procedures at the fundamental wavelength 1368 nm; d33 values in the range 0.2–3.3 pm/V were obtained, depending on the chromophore and on its molar content. The dependence of d33 on the molar content of chromophore was investigated in the two cases.

Six new side-chain polyurethanes with large molecular hyperpolarizabilities were synthesized by reaction of ethylenic and/or azo bridged push-pull chromophoric monomers with tolylene 2,4-diisocyanate. The NLO-phores show different conjugation pathway but analogous donor/withdrawing substituents. The chemical and thermal properties of the chromophores and of the polymers were examined. Evaluation of the second order NLO properties was performed by EFISH determination of mu beta on the monomers, and by SHG measurements on some amorphous thin films obtained from polymers through spin-coating technique. (c) 2004 Elsevier B.V. All rights reserved.

Summary: Condensation polymers based on two different NLO-active chromophores, namely 2-[4-[(4-N,N-dihydroxyethylamino)phenylazo]phenyl]-5(6)-nitrobenzimidazole (BZI) and 2-[4-(4-N,N-dihydroxyethylamino)phenylazo]- 4,5-dicyanoimidazole (IMI), have been synthesized and their basic properties measured. The second order NLO properties of poled polymers were investigated by SHG procedures at different temperatures (35, 65 and 85 °C) and exposure times. Resonance free d33 coefficients (lambda = 1368 nm) took values in the range 1.8–4.0 pm/V, but the time stability of their SHG signal was fairly acceptable, particularly for the high Tg (e.g. 188 °C) polymer for which a relaxation time (at 25 °C) of 2.8 years has been determined.

Femtosecond fluorescence upconversion experiments have been performed on Auramine O (a diphenylmethane dye) in polymethylmethacrylate (PMMA) and in hybrid organic/inorganic solgel based films.All the investigated samples showed a fast decay (few picoseconds) and a long decay (hundreds of picoseconds). The fast components are representative of the rapid cooling of the excess excitation energy to the matrices. The long components are representative of the excited-state lifetime of the probed molecules. Auramine O in solid matrices showed lifetimes longer than in liquid solutions. Torsional diffusion motions of the two phenyl rings of the molecule are held responsible for the excited-state dynamics.A dynamic Stokes shift has been observed for all samples. The lack of a rise time when detection was on the red side is explained in terms of an adiabatic coupling between emissive and nonemissive excited states, as is the case of liquid solutions. Different spectral shifts in PMMA and hybrid glasses have been measured. A different coupling between the emissive and nonemissive excited states for the two types of matrices is considered.

New polymers for second-order nonlinear optical (NLO) applications were synthesized and characterized. They were distinguished by the presence of chromophore groups, with various molecular hyperpolarizability values, used as pendants on substantially rigid backbones. The polymers were prepared through the reaction of tolylene-2,4-diisocyanate, or a suitable alkyloxyphthaloyl dichloride, with the N,N-diethanol-4-(phenyl) group azo-linked to a nitrofluorenone, nitrostilbene, nitrooxadiazole, or nitrothiadiazole moiety. The polymers exhibited good thermal stability, high glass-transition temperatures, and an absence of crystallinity. The second-order NLO properties of thin, transparent poled films, prepared by spin coating and thermal corona poling, were investigated for some of the polymers. The second harmonic coefficients, ranging between 18 and 25 pm/V, depended more on the alignment of the chromophore groups along the direction of the poling field than on their molecular hyperpolarizability. The temporal stability of the NLO properties of the polymers was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3013–3022, 2004

Full Paper: Functionalized second-order nonlinear optical (NLO) thiopene copolymers were synthesized. Two elegant syntheses based on the post-functionalization of polymeric precursors obtained by oxidative polymerization were developed, leading to copolymers that proved to be fully soluble in common organic solvents. The new materials were characterized by NMR, FT-IR, and UV-vis spectroscopies, gel permeation chromotography (GPC), and thermogravimetric analysis (TGA). Moreover, the NLO activity of the new materials, as determined by corona poling alignment and second harmonic generation (SHG) measurements, showed a good agreement between the second-order NLO coefficient and the chromophore concentration.

Three organometallic homopolymers and three copolymers have been obtained, by reacting, respectively, cyclopalladated dinuclear complexes with a polymeric backbone, and by radical copolymerization of cyclopalladated acrylic monomers and methyl methacrylate. Taking into account thermal behaviour and solubility, the copolymers, which display good second order nonlinear optical activity, seem to be the most promising for applications within the new metallated macromolecules. Macroscopic nonlinear optical coefficients d 33 have been determined on spin-coated corona-poled thin films by means of Second Harmonic Generation (SHG) measurements at the wavelength of 1064 nm.

The degradation mechanisms of Reverse Bias (RB) stressed Dye Solar Cells (DSCs), sensitized with cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)bis-tetrabutylammonium (N719, Red Dye) and with cis-dicyano-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) (Ru505, Orange Dye) have been studied by means of resonance micro-Raman and UV-Vis spectroscopy. For N719 sensitized devices, the visible degradation induced by the stress tests involves both electrolytic solution and the sensitizer: the electrolyte suffers gas bubble formation and loss of solvent, while the dye cannot be regenerated and undergoes irreversible chemical changes. Confocal Raman imaging and UV-Vis absorption spectra confirmed that in regions where the electrolyte was absent, the detachment of the thiocyanate ligand (SCN−) from the dye is favored. On the other hand, measurements carried out on DSCs realized with the bis-cyano dye (Ru505) do not show dye modifications during the RB stress. We also clarify that the apparent N719 dye bleaching in particular zones of the cell active area, is not related to dye desorption from the TiO2 layer, but to loss of solvent and to dye chemical changes, which are responsible for a characteristic blue shift in the absorption spectrum.

We report on the optical properties of two dye molecules absorbing in the near infrared region (0.8-1.1 mu m) and emitting up to 1.3 mu m. The chromophores are embedded in hybrid organic/inorganic silicon-based films synthesized by a modified sol-gel technique. Femtosecond time-resolved emission spectra have been measured in order to determine the effect of the solid cage on the excited state dynamics of the trapped molecules. For comparison, measurements in different solvents are reported and an estimation of the relative quantum efficiency in solid glassy material with respect to liquid solutions is given. Measurements are discussed in terms of physical and chemical interactions with the host matrix.

Filopodia are thin cell extensions sensing the environment. They play an essential role during cell migration, cell-cell or cell-matrix adhesion, by initiating contacts and conveying signals to the cell cortex. Pathogenic microorganisms can hijack filopodia to invade cells by inducing their retraction towards the cell body. Because their dynamics depend on a discrete number of actin filaments, filopodia provide a model of choice to study elementary events linked to adhesion and downstream signaling. However, the determinants controlling filopodial sensing are not well characterized. Here, we have used beads functionalized with different ligands that triggered filopodial retraction when contacting filopodia of epithelial cells. With optical tweezers (OTs), we were able to measure forces stalling the retraction of a single filopodium. We found that the filopodial stall force depends on the coating of the bead. Stall forces reached 8 pN for beads coated with the β1- integrin ligand Yersinia Invasin, while retraction was stopped with a higher force of 15 pN when beads were functionalized with carboxyl groups. In all cases, stall forces increased in correlation with the density of ligands contacting filopodial tips and were independent of the optical trap stiffness. Unexpectedly, a discrete and small number of Shigella type three secretion systems induced stall forces of 10 pN. These results suggest that the number of receptor-ligand interactions at the filopodial tip determines the maximal retraction force exerted by filopodia but a discrete number of clustered receptors is sufficient to induce high retraction stall forces.

A guest-host polymer system with potential use in electro-optic devices is discussed. The polymer host is a high Tg, fully aromatic polyimide and the guest chromophore is disperse red 19. Relaxation mechanisms of polar order after electric field alignment procedure have been investigated by measuring the isothermal decay of the macroscopic nonlinear optical coefficient d333 at different temperatures below glass transition temperature (Tg), upon the removal of the poling electric field. All the decay curves can be fitted by a double exponential function. Below Tg, the slower relaxation time shows an Arrhenius temperature dependence. An extrapolation to room temperature allows to predict the time stability which results to be longer than 30years. In addition, absorption spectra measurements of the films were performed before and immediately after poling procedure to estimate independently the polar order of the dipoles through the decrease of the absorption coefficients.

Using spectral compression by second-harmonic generation we generate pulses with 10÷15 cmμ1 linewidth, multi-μJ energy and broad tunability from 330 to 510 nm. This source is ideally suited as Raman pump for Stimulated Raman Scattering.