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Aims: This work investigates the photoluminescence properties of poly(3- octylthiophene), namely P3OT films, under excitation power and time light expositions. When exposed to monochromatic illumination, the degradation mechanism of P3OT films is precise in environmental conditions. However, in some environmental controlled or non-environmental conditions, the quenching luminescence of P3OT subject to monochromatic light excitation is not fully understood. In this context, it is necessary to understand what causes quenching luminescence of P3OT films under environmental conditions. Methods: The P3OT was synthesized by chronocoulometry, using tetraethylammonium tetrafluoroborate and lithium perchlorate as supporting electrolytes, and after it is deposited on a conductive substrate of fluoride-doped tin oxide (FTO). The films were synthesized and maintained under an argon atmosphere, and their thickness is dependent on the charge. The characterisation was achieved by applying techniques like UV-Vis absorption spectroscopy, photoluminescence, and emission ellipsometry. Results: The UV-Vis absorption measurements demonstrated a different interaction of polymer/ dopant due to the polaronic band. The results showed that photoluminescence quenching with time is a behaviour caused by energy transfer between quinone chains and pristine chains of the P3OT. The polarised emission measurements corroborate the hypothesis of energy transfer between chains. The emission ellipsometry technique was used to understand energy transfer processes and other properties. The self-absorption phenomenon and integrated PL investigation of the P3OT emission elucidated the mechanism involved in the observed properties. Conclusion: Besides that, the results show that photoluminescence quenching happens in nonenvironmental and environmental conditions, corroborating the hypothesis that PL quenching occurs because self-absorption phenomena influence the energy transfer mechanism.

In situGIWAXS experiments reveal that the presence of RGO decreases the formation rate of the perovskite, increases the grain size, and improves the stability of solar cells.

In this paper, we report a simple procedure to decouple effects from temperature and volume on the emission properties of thin films of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV). This procedure consists of applying a positive pressure close to the β-relaxation temperature, Tβ (∼220 K), of MEH-PPV, which controls the molecular movement to retain a disordered state for the polymer chains even after the sample is cooled from room temperature. Such decoupling could be confirmed by calculating the photoluminescence (PL) spectra line shape using a semi-empirical model based on molecular exciton and Franck-Condon transitions, and with electron-vibrational modes coupling being parameterized with the Huang-Rhys factor. We also show that the decoupling between temperature and volume effects does not occur if the molecular movement is restricted either by thermal annealing or by depositing the MEH-PPV film on a rigid substrate. This latter finding may be exploited in designing thermally stable devices.

Female mimicry by males is a widespread phenomenon in several taxa and may be involved in aggression avoidance or facilitated access to resources. In early developmental stages, female mimicry may be a mechanism involved in signalling sexual immaturity or, when coupled with strategies related to visual camouflage, may be involved in the avoidance of male-male agonistic interactions. Here, we addressed whether the delayed colour maturation of a sexual ornament in males of Mnesarete pudica damselflies might be a case of crypsis, female mimicry or both. We analysed how conspecifics and predators perceive the pigmented wings of juvenile males by contrasting the wing spectra against a savannah background and the wings of both juvenile and sexually mature males and females. Our results based on the modelled visual system of conspecifics and predators suggest that the colour maturation of juvenile males may function as both crypsis and female mimicry. We discuss whether these results related to age- and sexual-dichromatism might be a mechanism to avoid unwanted intraspecific interactions or to avoid territorial and aggressive males. We conclude that the female mimicry and crypsis in juvenile males of M. pudica are mechanisms involved in avoidance of predators and unwanted intraspecific interactions, and the signalling of sexual maturity.

Controlled drug release holds promise to revolutionize medicine, particularly if short-term and long-term release can be combined in a single system. We present here a new pulsatile release system,...

The rationale of this paper is to shed some light on the origin of the optical response of two similar chiral fluorene copolymers in correlation with their vibrational modes, to understand how a chiral center placed in a ramification affects the optical properties of the main chain. Various spectroscopic ellipsometric techniques, in the scope of the Stokes theory were used to characterize the optical-vibrational behavior of the polyfluorenes: ellipsometry in emission (EE), transmission (TE), and Raman (ERS). The results showed that the optical activity and the emission of the circularly polarized light depends substantially on the interaction of the chiral carbon in the ramification and the main chain through specific optically active vibrational modes, for each sample. One interesting achievement was to find the absolute dextrorotatory configuration of the studied molecules, that could induce a helicoidal structure to the entire material.

The use of ultraviolet (UV) and blue irradiation to sterilize surfaces is well established, but commercial applications would be enhanced if the light source is replaced with ambient light. In this paper, it is shown that nanofibers can be explored as an alternative methodology to UV and blue irradiation for bacterial inactivation. It is demonstrated that this is indeed possible using spun nanofibers of poly[lactic-co-(glycolic acid)] (PLGA). This work shows that PLGA spun scaffolds can promote photoinactivation of Staphylococcus aureus and Escherichia coli bacteria with ambient light or with laser irradiation at 630 nm. With the optimized scaffold composition of PLGA85:15 nanofibers, the minimum intensity required to kill the bacteria is much lower than in antimicrobial blue light applications. The enhanced effect introduced by PLGA scaffolds is due to their nanofiber structures since PLGA spun nanofibers were able to inactivate both S. aureus and E. coli bacteria, but cast films had no effect. These findings pave the way for an entirely different method to sterilize surfaces, which is less costly and environmentally friendly than current procedures. In addition, the scaffolds could also be used in cancer treatment with fewer side effects since photosensitizers are not required.

In this work, energy transfer processes are quantified to poly(3-hexylthiophene) (P3HT) polymeric films synthesized electrochemically. Results obtained are linked to pristine chains, mixed chains (composite by quinone and pristine chains) and oligomers in the polymeric films. Energy transfer processes and photophysical equations to P3HT films were based on photoluminescence and Stokes Parameters Spectroscopy experiments. We quantified the energy transfer photo exciting oligomer molecules. We showed that ca. 80% absorption energy (oligomers) is transferred to other species (quinone and pristine chains). Furthermore, energy transfer was correlated with polymeric electrochemical cycles.

We report on the synthesis of poly(styrene sulphonate) (PSS) doped with iron ions (PSS:Fe) and its electrical properties in J-Field Effect Transistors (J-FET). PSS:Fe films exhibited enhanced ferroelectric and conductance in comparison with non-doped PSS films, with a conductivity of 4.47 10−6 S/m. In comparison with traditional ferroelectric polymers, such as poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], PSS:Fe films had coercive fields three orders of magnitude smaller and remnant polarization six orders of magnitude higher. When operated with a negative gate voltage (VG), the drain current (ID) increased significantly, while positive gate voltages reduced the conductor channel and decreased ID. The proposed in-plane geometry with PSS:Fe monolayer films exhibits suitable ferroeletricity characteristics.

This paper presents the results of a study conducted on the interaction between curcumin, a compound with several biomedical applications in traditional and modern medicine, and the acrylic polymers poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate), through photophysical experiments in curcumin/acrylic polymers casting films. Optical absorption intensity at ~340 nm increases relatively to its maximum at ~417 nm when the amount of curcumin in the polymeric film decreases, due to a significant change in the concentration of the isomers cis- or trans-form of curcumin, regardless of the acrylic polymer. Fluorescence (FL) spectra of the films depend on the curcumin concentration in the matrix with well-resolved line shape. They show two distinct bands, one at ~525 nm, for higher curcumin concentration (5.00 mmol.L-1), related to the aggregated curcumin species, and another at ~465 nm, for lower concentration of curcumin (0.10 mmol.L-1), related to the effects of the solvent on the conformational structure of the curcumin molecule and the presence of the trans-form of curcumin. The parameter Kagg, related to the contribution of the aggregated curcumin, shows the influence of the polymeric lateral chain length of the matrix in the de-aggregation of the curcumin. The Huang-Rhys factor indicates that curcumin aggregated species are conformationally more stable, and that the isolate species depends on the chemical environment and the matrix/curcumin interaction, decreasing its conformational degrees of freedom. Arrhenius plots, obtained via FL experiment in function of the sample temperature, show that, for higher curcumin concentration, the value for the relaxation energy process is not well defined, due the decrease in the interaction between the matrix and the curcumin molecules. With these results, it is possible to infer that the interaction matrix/curcumin must occur via lateral chemical alkyl groups.

In this paper, we introduce simple procedures not only to enhance the polarized photoluminescence (PL) of poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) films but also to vary the relative concentrat...

Photoluminescence (PL) and electroluminescence (EL) spectra were used to probe the thermal relaxation processes of the poly(9,9'-n-dihexyl-2,7-fluorenediiylvinylene-alt-1,4-phenylenevinylene) (LaPPS16) electroluminescent polymer. A theoretical model of molecular excitons and Franck-Condon transitions were used to analyze the line shape of the radiative transitions. It was possible to correlate directly the electron-vibrational mode coupling, i.e., the Huang-Rhys parameter, and the polymer relaxation processes due to the effects of molecular dynamics on the electronic states. The results showed different dependences of the thermal relaxation process on PL and on EL due to the molecular dynamics restraints of LaPPS16. This could explain the efficiency variation in organic light emitting diodes where the external electric field would decrease the degrees of freedom of the polymer and activate specific non-radiative channels. Molecular relaxation temperatures of the LaPPS16 polymer are proposed.

In the present paper, we optimize the chemical synthesis of guest/host poly(styrene sulphonate) (PSS) doped with neodymium ions (Nd 3 + ) using chemometric and univariate procedure for volume variables of acid form of PSS and neodymium chloride (NdCl 3 ) confirmed by FTIR experiment. In optimization procedure, the exchange counter-ions H + by Nd 3 + increases, substantially, the luminescence quantum yield, up to 75%, to 4 F 3/2 → 4 I 11/2 transition of Nd 3 + . Results show the possibility of using the present material as an efficient optical emission material, in the near infrared range, by adding polymer mechanical properties.

γ, β and α relaxation processes in nylon 6,6 were studied by means of Raman spectroscopy, being a vibrational spectroscopic technique sensitive to chemical groups in the polymeric matrix and therefore sensitive to temperature dependent changes in the molecular configuration of the polymeric sample probed. Through a temperature-dependent Raman spectroscopic experiment within the temperature range from -120 °C to +120 °C we determined temperature-dependent changes of peak parameters of the Raman bands associated with the C O, C C, and N H stretching vibrations, being able to determine the temperature ranges where changes occur which can be associated with relaxation processes, which result to be in accordance with published experimental results obtained by thermodynamic and mechanical techniques, i.e. macroscopic techniques.

We studied the absorption line-shape of poly(p-phenylenevinylene) (PPV) films deposited via spin coating and Langmuir-Blodgett techniques with the intent of identifying the conjugation length distribution in these two types of films, a key morphological aspect of conjugated polymer films. We treated the excitons in the polymer as independent oligomer excitons and modeled the absorption spectra of the individual oligomers using simple expressions for the oligomer size dependence of the gap energy, the line-broadening factor, the transition dipole moment and the Huang-Rhys parameter. We validated these expressions by independent measurements on phenyl-based oligomers and Density Functional Theory calculations. Our results show clear evidence that, for both types of PPV films, the conjugation length distribution depends exponentially on the segment size. Our results also set a lower limit, of about ten repeat units, for the maximum exciton length of three different phenyl-based oligomers.

This article presents a successfully development of hybrid functional nanomaterials composed of Protoporphyrin-IX/Halloysite nanotubes (PpIX/HNTs), in which the PpIX molecules were adsorbed on the surface of the HNTs at different degree of aggregation. This article also presents a possible explanation for the PpIX adsorption by the HNTs surface and, moreover, the results show that the PpIX molecules adsorption on the HNTs surfaces, and its degree of aggregation, can be controlled by changing the ratio between PpIX and HNTs concentrations. Interestingly, from photodegradation experiments, it is observed that, after the photodegradadion of isolated monomers, the PL spectra and the photodegradation curves show that there is a ratio between the amount of residual monomers and dimers in which the PpIX/HNTs photodegradation decreases significantly, leading to a more photostable system. Therefore, these PpIX/HNTs systems can lead to the development of more efficient porphyrin-based devices and processes, and help to understand the processes of aggregation and formation of porphyrin supramolecular structures.

In the present work, we have studied the liquid crystalline properties of a luminescent molecule, which presents smectic mesophases, using the emission ellipsometry technique. A methodology with photoselection of the excitation light to improve the experiment is presented. An empirical model is proposed to explain the experimental results. The Stokes parameters of the emitted light allowed the correlation of changes in the polarization degree, ellipticity angle, and rotation angle with phase transitions.

Self-assembled cadmium sulfide (CdS) thin solid films were synthesized by chemical bath deposition (CBD) technique for different deposition times (20 min.–24 h) on transparent and flexible polyester substrates using sodium acetate complex agent. CBD-CdS films were also deposited on glass (BK7) and quartz substrates, as reference. CBD-CdS films on polyester substrate showed a homogeneous deposition, reduction of chemical or structural defects (green emission), and large photoluminescence efficiency in comparison of CBD-CdS films deposited on Si-based substrates. Simulation of PL temperature dependence for polyester CdS films using the rate equation for the carrier population showed the presence of two decay pathways due to cadmium and sulphide defects at crystallite.

Herein a useful methodology to study optical properties of cholesteric liquid crystals (Ch-LC) is proposed by using the Fourier decomposition ellipsometry technique to calculate the Stokes parameters of transmitted and reflected light in the UV–Vis spectral range. Combining Bragg reflection and optical activity we were able to obtain ∼100% of linear or circular light polarization from the Ch-LC sample using achromatic and non-polarized light source. The photonic bandgap and the polarization components can be controlled with the temperature as a result of alterations in the helix pitch of the cholesteric phase. Finally, it is demonstrated the correlation between the dissymmetry factor ( g ) calculated via the Stokes parameter S 3 and the reflection spectrum. The data revealed that the maximum value of S 3 is not coincident with the peak of maximum reflection. The reflected or transmitted light analysis via Stokes parameters obtained by ellipsometry showed an alternative and low cost method for optical characterization in Ch-LC.

We report on a phenomenological, theoretical model to calculate the rate constants and activation energies for the thermal conversion reactions from poly(xylylidene tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylenevinylene) (PPV) using the optical absorption spectra of spin-coated films. The probabilities of electron transitions were calculated considering Franck-Condon states with a Gaussian distribution of conjugated segments and molecular excitons. The dependence on the conjugation degree (n) for the energy gap, transition dipole moment, and electron-phonon coupling were obtained semiempirically using published data for PPV. Fitting was performed for the C-C stretching of the aromatic ring 1550 cm(-1), for it is considered the most optically active. The isotherms for consumption and formation of PPV segments were fitted using a first-order and consecutive reactions, respectively. With this modeling we could identify the most probable reactions, where the formation of longer PPV segments n ≥ 3 occurs only via reactions from smaller conjugated segments (i.e., n = 1 and 2). The activation energies tend to decrease with longer conjugation lengths. Significantly, the modeling allows us to predict the conversion temperature and chemical composition yielding a predefined distribution of conjugated segments, which can be applied to any polymer undergoing thermal conversion, decomposition, or photo-oxidation.

Curcumin ((1,7-bis-(4-hidroxi-3-metoxifenil)-1,6-heptadieno-3,5-diona)), is a natural yellow-orange polyphenol dye, obtained from Curcuma longa rhizomes, with vast potential in the biotechnology field, such as anti - inflammatory and cancer preventive properties, and a very environmental-sensible structure, mostly resulting in aggregate formations, with low solubility in aqueous solvents and remarkable pH dependence. Hence, it is essential to comprehend its aggregation mechanisms, optical properties and conformational equilibrium to develop curcumin-based drugs and biomaterials for several applications. With the purpose of understand such concepts and its properties, the results presented in this work, obtained through spectroscopic measurements and the Hill's modeling, show a conformational equilibrium, driven by pH, between the enol-enolate and aggregated forms in curcumin, and the respective energy transfer processes between these species. Additionally, the photophysical mechanisms for the energy transfer between aggregated forms, observed with the ellipsometry measurements, showed an "all-or-nothing" character, pointing to a very complex conformation for curcumin aggregates.

Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate recognition and mate quality functions in many animal taxa. We investigated the role of wing ultra-violet reflection, fluorescence emission, and pigmentation on age and sexual signals in the damselfly Mnesarete pudica. In this species, wings are sexually dimorphic in colour and exhibit age dependency: males and females show a smoky black colouration when young, turning red in mature males while it turns brown in females. First, we investigated wing UV patterns through reflectance and emission spectra. Second, behavioural experiments were undertaken to show male and female responses to manipulated wing pigmentation and experimentally reduced UV (UV-). Reflectance spectra of the wings of juvenile and mature males and females were used to show the differences between controls and individuals with manipulated colouration used in the behavioural experiment. UV-reduced, females with wings painted red, and control males and females were tethered and presented to conspecific males and females, and their behavioral responses were recorded. The male red wing pigmentation and females with red wings elicited an aggressive response in territorial males and a sexual response in females. Both males and females showed neutral responses towards individuals with reduced UV. Wing signals of juvenile individuals also provoked neutral responses. These results suggest that UV, together with pigmentation, plays a role during mate recognition in males and females. Other than butterflies and spiders, it seems that fluorescence signals and UV reflectance can also be part of communication in odonates.

The emission ellipsometry technique was applied to the donor–acceptor structure, poly[9,9′-dioctyl-2,7-fluorenevinylene-alt-4,7-(di-2,5-thienyl)-2,1,3-benzothiadiazole], to quantify the energy transferred from the donor (fluorene) to the acceptor (thiophene–benzothiadiazole–thiophene). The relative contributions to the total emission from both donor and acceptor were determined and also the amount of the emitting species that lost coherence with the polarization of the excitation light. The results were discussed in terms of energy transfer via multiphonon processes.

In the present paper the layer-by-layer self-assembly (LbL) technique was used to obtain poly( p -phenylenevinylene) (PPV) films exchanging the counter-ion Cl of the poly(xylylidene tetrahydrothiophenium) (PTHT ) precursor polymer by Congo Red (CR) azodye. The objective of the present paper is to study the azodye photoisomerization trans → cis → trans process as a function of the PPV thermal annealing procedure. The LbL PTHT/CR films were thermally converted into LbL PPV/CR films at low (110 °C) and conventional (230 °C) temperatures, and characterized through both absorption and emission techniques. We found that the unexpected emission band above 650 nm, attributed to the azodye, for LbL PPV/CR film thermally converted at lower temperature (110 °C) is an evidence of the considerable decrease of CR degradation in the polymeric matrix. Emission anisotropy and selective photoluminescence were carried out to characterize qualitatively the exciton energy transfer.

In this paper, we study the importance of the non-homogeneity energy dispersion on absorption line-shape of luminescent polymers. The optical transition probability was calculated based on the molecular exciton model, Franck–Condon states, Gaussian distribution of non-entangled chains with conjugate degree n , semi-empirical parameterization of energy gap, electric dipole moment, and electron-vibrational mode coupling. Based on the approach of the energy gap functional dependence 1/ n , the inclusion of the non-homogeneity energy dispersion 1/ n 2 is essential to obtain good experimental data agreement, mainly, where the absorption spectra display peaks width of about 65 meV. For unresolved absorption spectra, such as those observed for a large number of conjugated polymers processed via spin-coating technique, for example, the non-homogeneity energy dispersion parameterization is not significant. Results were supported by the application of the model for poly ( p -phenylene vinylene) films.

This paper reports the influence of the molecular relaxation temperature and electric field on the emission efficiency of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) in Organic Light-Emitting Diode (OLED) structure. We observe that the photoluminescence (PL) depends on the OLED polarization (forward and reverse) and on MEH-PPV molecular β-relaxation ( T β ∼ 220 K) and α-relaxation ( T α ∼ 330 K) temperatures. Above T β unbalance in charge carrier concentration in the device have a significant effect on the emission efficiency. The exciton energy transfer as a function of the sample temperature was determined using emission ellipsometry within the Stokes’ theory scope. Regardless of the OLED voltage polarization, the emission is partially linearly polarized and the polarization degree decreases significantly above T β and T α temperatures. Finally, we propose an approach to enhance the emission efficiency of luminescence polymers by controlling the molecular relaxation temperatures of the multilayer polymer OLEDs.

Poly( p -phenylene vinylene) (PPV) thin films were produced by layer-by-layer (LbL) method, using soluble PPV-precursor and dodecylbenzenesulfonate salt (DBS). The amount of deposited layers strongly influences the optical properties of the thermally converted PPV film. The absorbance and luminescence spectra of ultra-thin films (consisting of only two or three PPV layers) are shifted to smaller wavelengths with respect to spectra of thicker films. This is related to the smaller average conjugation length of polymer chains, resulting in a higher HOMO–LUMO gap energy of the material. However, if a thick film is produced by repeating the deposition process and thermal conversion of ultra-thin layers, the optical spectra are still displaced to higher energies in comparison with those of thicker films produced by the conventional continuous deposition of layers. This result enabled the production of multilayered polymeric films with modulated energy profile, taking the number of deposited layers as the only variable in the manufacturing process of the structure. The aim is to guide the excitation to specific regions of the material through the Forster-type energy transfer processes. Such systems can be used at interfaces electrode/polymer and/or electrode/polymeric active layers in order to improve the performance of organic optoelectronic devices.

In this work we simulate the photoluminescence (PL) spectra of BDMO-PPV thin films prepared by spin-coating technique on glass and on copper, as a function of temperature (12–300 K). Simulations were done using two theoretical models based on (i) the SSH theory where the line shape of the purely electronic transition is partly generated by localized states and partly by delocalized states and (ii) the semi-empirical model containing the coupling between localized molecular excitons and vibrational modes in Franck–Condon approach. Four active vibrational modes have been considered: C–C stretching coupled to a C–H bending of the phenyl ring at 1111.5 cm −1 , inter-rings C–C stretching at 1282.2 cm −1 , CC stretching coupled to a C–H bending of the vinyl group at 1309.3 cm −1 , C–C stretching of the phenyl ring at 1580.2 cm −1 . Additional vibrational mode of 403 cm −1 associated with C–C–C out-of-plane bending allowed leastwise for this material to adjust well with the characteristic asymmetry of the purely electronic transition. Finally, application of theoretical models are strongly dependent on the well-resolved PL spectra, i.e., electronic transition peak presented a relatively thinner HWHM and an asymmetric line shape.

This article discusses a strategy to reduce the degradation of a poly(p-phenylene vinylene) (PPV) film at the interface with an indium–tin oxide (ITO) electrode. It consists of using a less aggressive leaving group, the sodium dodecylbenzenesulfonate salt (DBS), in the chemical synthesis of PPV starting with the polymer precursor, and performing the thermal conversion into PPV at a lower temperature (100 °C) than in the conventional synthesis. The absorbance spectrum for an ITO/PPV + DBS film indicated that the polymer is less degraded and has the emission efficiency increased by ca. 4.5 times in comparison to ITO/PPV films obtained with the conventional procedures, i.e., with thermal conversion at 200 °C, in vacuum, during 2 h. The main reason for the enhanced performance of the route reported in this article is a decrease in the oxygen concentration at the ITO/PPV interface, as inferred with X-ray Photoelectron Spectroscopy which corroborates the optical properties.

In this work, poly(3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueous media through the oxidation of the monomer, (3-octylthiophene), using a standard three-electrode cell in acetonitrile with 0.05 mol L S1 LiClO4 or 0.05 mol L S1 Et4NBF4. The polymeric films were deposited on fluorine tin oxide (FTO). The partial dedoping was obtained in NH4OH solution, providing a good chemical stability of the formed material. The films obtained through this method have been characterized by Fourier-transform infrared spectroscopy (FT-IR), electron paramagnetic resonance (EPR), UV–Vis absorption, and photoluminescence (PL) spectroscopy. The FT-IR and EPR spectra together gave the results that led to characterization of two structures (pristine and non-pristine forms of thiophene rings) while forming the P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non-pristine structures) in the polymeric film. Their bands in the PL spectra are wide and asymmetric and their adjustments by Gaussian functions was necessary; this was the main indication that there are two distinct contributions to the emission spectra. These two contributions are attributed to the emission by mixed chains (Gaussian centered at higher energy) and by pristine chains (Gaussian of lower energy) present in the formed polymeric material. Copyright 2010 John Wiley & Sons, Ltd.

This work addresses the effects of Gamma radiation on the absorbance and emission properties in layer-by-layer (LbL) poly( p -phenylene vinylene) (PPV)/dodecylbenzenesulfonate (DBS) thin films. The LbL PPV/DBS films were irradiated with 2 Gy and 100 Gy doses, using a 60 Co source of Gamma radiation. The effects of irradiation on absorbance and emission of PPV were discussed. The new methodology applied to analyze the effects of radiation on luminescent conjugated polymers provides the possibility to use this material in large-area, low-cost dosimeter sensors.

The discovery of an alternative route to convert poly(xylyliden tetrahydrothiophenium chloride) (PTHT) into poly( p -phenylene vinylene) (PPV) using dodecylbenzenesulfonate (DBS) has allowed the formation of ultrathin films with unprecedented control of architecture and emission properties. In this work, we show that this route may be performed with several sufonated compounds where RSO 3 − replaces the counter-ion (C1 − ) of PTHT, some of which are even more efficient than DBS. Spin-coating films were produced from PTHT and azo-dye molecules, an azo-polymer and organic salts as counter-ions of PTHT. The effects of the thermal annealing step of PTHT / RSO 3 − films at 110 and 230 °C were monitored by measuring the absorption and emission spectra. The results indicate that the exchange of the counter-ion Cl − of PTHT by a linear long chain with RSO 3 − group is a general procedure to obtain PPV polymer at lower conversion temperature (ca. 110 °C) with significant increase in the emission efficiency, regardless of the chemical position and the number of sulfonate groups. With the enhanced emission caused by Congo Red and Tinopal as counter-ions, it is demonstrated that the new synthetic route is entirely generic, which may allow accurate control of conversion and emission properties.

International audience; Thienylene–dialkoxyphenylene copolymers with polar side chains are soluble in most organic solvents and exhibit excellent glass adhesion properties, allowing the formation of homogeneous thin films on glass, quartz, and other substrates by spin coating. The electrochemical and optical properties of thin films of this material are studied in this work. The calculated band gap derived from electrochemical data (2.34 eV) is in good agreement with that observed from the UV–vis spectrum edge (2.25 eV). The analysis of the emission properties reveals the strong dependence on temperature of the electron coupling with different vibrational modes in the formation of the vibronic bands.

This Letter reports about the molecular alignment effects on absorbance and emission properties of a new compound based on 2,1,3-benzothiadiazole guested in liquid crystals. The molecular ordering is available for different chromophore concentrations. Despite of the increasing in molecular disorder above the concentration of 0.20%, samples always present a high degree of linear polarization in fluorescence. A considerable amount of polarized emission is observed during the isotropic phase (T > 58 °C), which is attributed to emission of light by aligned molecules before loosing the coherence among them. Finally, we demonstrate the feasibility of ellipsometry technique to investigate phase transitions in fluorescent systems.

In this work, we have studied the surface morphology of photo-irradiated poly(p-phenylene vinylene) (PPV) thin films by using atomic force microscopy (AFM). We have analyzed the first-order statistical parameters, the height distribution and the distance between selected peaks. The second-order statistical analysis was introduced calculating the auto-covariance function to determine the correlation length between heights. We have observed that the photo-irradiation process produces a surface topology more homogeneous and isotropic such as a normal surface. In addition, the polymer surface irradiation can be used as a new methodology to obtain materials optically modified.

The control of emission properties in luminescent polymers such as poly(p-phenylene vinylene) (PPV) is important for various applications, and may be achieved with suitable molecular architectures in nanostructured films. This paper reports on optical properties of PPV films, using ellipsometry measurements for emitted light in the scope of the Stokes' theory. Organized PPV films obtained with the Langmuir-Blodgett (LB) method exhibited high degree of polarization for the emitted light, while cast films emitted mainly non-polarized light. From ellipsometry data, a secondary structure was inferred for poly(xylylidene tetrahydrothiophenium) chloride (PTHT), a PPV precursor, in solution, which is retained only to a small extent in the PPV cast film as thermal conversion was performed close to the glass transition temperature of PPV. On the other hand, a higher intensity of emitted light with circular polarization was observed for the LB film, which is attributed to PPV molecular secondary structure that was enhanced during the LB film deposition. Circular dichroism experiments were performed to corroborate this hypothesis. It is suggested that such a secondary structure has not been predicted in theoretical models for PPV because possible conformational changes induced in the processing steps are not taken into account.

In attempts to obtain poly( p -phenylene vinylene) (PPV) molecules without intermacromolecular aggregation two strategies were employed: the addition of a strong electrolyte, lithium chloride, to the solution of the precursor, or/and the preparation of solid solutions from co-dissolved precursor and poly(vinyl alcohol) (PVA). The effects on the thermal conversion process of PPV were studied. Complete isolation of the PPV chains was not attained, but a significant degree of chain separation was achieved, as demonstrated by spectroscopic data. The main observations were that strong intermacromolecular forces operate during the PPV elimination step, resulting in simultaneous aggregation with the formation of the final chains. The relative emission efficiency increases up to 115% for PPV and PPV:PVA films when 0.7% and 1.4% of LiCl, respectively, are added and lower conversion temperature (100 °C) procedure is employed. In the case of total annealing procedure (230 °C) the emission efficiency increases 65% for PPV:PVA film with 0.7% of LiCl. For PPV:LiCl films, this parameter decreases substantially (∼11%) when the salt concentration increases above 10%.

This work reports on the use of the ellipsometry technique to study the polarization state of emitted light by poly[2-methoxy-5-((2′-ethylhexyl)oxy)-1,4-phenylenevinylene] (MEHPPV) in solution. The sample presents a partially linear-polarized fluorescence not affected by molecular-concentration, excitation-laser power, probe-wavelength and cuvette-material. The independence of the polarization degree with these variables and its variation with solvent viscosity suggest that the effect can be understood, assuming the existence of a steady regime where light is absorbed and reemitted faster than the average molecular diffusion time. Moreover, we verified that the polarized emission is also observed by other polymers in solution.

This work reports the structural and spectroscopy characterization of poly(styrene sulfonate) (PSS) films doped with neodymium (Nd) ions. Nd–PSS films were processed using the acid of poly(styrene sulfonate) – H–PSS and neodymium nitrate – Nd(NO 3 ) 3 ; the maximum incorporation of Nd ions in the polymeric matrix was equal 19.3%. The absorption in the UV–Vis–NIR spectral region presents typical electronic transitions of Nd 3+ ions, with well resolved peaks. The infrared spectra present the transition bands of PSS with characteristic line shape broadening, and the presence of vibrational modes of N–O groups in the range of 1400–720 cm −1 , prove the permanence of Nd(NO 3 ) x , with x = 1, 2 and/or 3, in the H–PSS matrix. UV–Vis site selective photoluminescence data indicate that the incorporation of Nd 3+ introduces a blue shift in PSS emission (325–800 nm), decreasing the interaction between adjacent PSS lateral groups (aromatic rings). Nd 3+ reabsorption and energy transfer effects between the PSS matrix and Nd 3+ were also observed. The IR emission of Nd–PSS films at 1076 nm ( 4 F 3/2 → 4 I 11/2 ) present constant efficiency, independent on Nd 3+ concentration. The Judd–Ofelt theory was employed to analyze radiative properties. The excitation spectra prove the energy transfer between the polymeric matrix and Nd 3+ . Complex impedance data was used to probe relaxation processes during the charge transport within the polymeric matrix.