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Sensors for the detection of heavy metal ions in water are in high demand due to the danger they pose to both the environment and human health. Among their possible detection approaches, modulation of the photoluminescence of gold nanoclusters (AuNCs) is gaining wide interest as an alternative to classical analytical methods based on complex and high-cost instrumentation. In the present work, luminescent oxidized AuNCs emitting in both ultraviolet (UV) and visible (blue) regions were synthesized by pulsed laser ablation of a gold target in NaOH aqueous solution, followed by different bleaching processes. High-resolution electron microscopy and energy-dispersive X-ray scattering confirmed the presence of oxygen and gold in the transparent photoluminescent clusters, with an average diameter of about 3 nm. The potentialities of the bleached AuNCs colloidal dispersions for the detection of heavy metal ions were studied by evaluating the variation in photoluminescence in the presence of Cd2+, Pb2+, Hg2+ and CH3Hg+ ions. Different responses were observed in the UV and visible (blue) spectral regions. The intensity of blue emission decreased (no more than 10%) and saturated at concentrations higher than 20 ppb for all the heavy metal ions tested. In contrast, the UV band emission was remarkably affected in the presence of Hg2+ ions, thus leading to signal variations for concentrations well beyond 20 ppb (the concentration at which saturation occurs for other ions). The limit of detection for Hg2+ is about 3 ppb (15 nmol/L), and the photoluminescence intensity diminishes linearly by about 75% up to 600 ppb. The results are interpreted based on the ligand-free interaction, i.e., the metallophilic bonding formation of Hg2+ and Au+ oxide present on the surface of the UV-emitting nanoclusters.

Made available in DSpace on 2021-06-25T11:03:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Nowadays, flexible organic electronics are under intense investigation for environmentally friendly and biocompatible applications. One of the main components of electronic devices is the substrate, which gives support for building devices. There is great interest in the scientific community for the development of biocompatible and biodegradable substrates for the manufacture of these kinds of devices, aiming at technological and medical applications. In this work, we produced a flexible and transparent biosubstrate based on a gellan gum polymer by a solvent casting method to manufacture flexible organic light-emitting diodes (FOLEDs). The gellan substrate exhibited optical transparency of about 78% at 550 nm and 80% at 900 nm. In addition, the optimized indium tin oxide (ITO)/SiO2-coated gellan substrate exhibited a resistivity of 2.8 × 10-4 ω·cm and a sheet resistance of 11.2 ω/sq. These values are better or equal to those found in the literature for similar biosubstrates. Finally, the fabricated FOLEDs exhibited a maximum luminance of about 2327 cd/m2 and the current efficiency reached a maximum value of 2.9 cd/A. These characteristics reveal that this biosubstrate has interesting potential for applications in flexible green electronics, mainly due to its biocompatible properties and the results obtained by the developed FOLEDs. Grupo de Nanociência e Nanotecnologia (NANO) Departamento de Física Universidade Federal de Juiz de Fora (UFJF) Laboratório de Biopolímeros e Biomateriais (BIOPOLMAT) Departamento de Biotecnologia Universidade de Araraquara (UNIARA) Laboratório de Optoeletrônica Molecular (LOEM) Departamento de Física Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) Departamento de Química Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) Instituto de Química Universidade Estatual Paulista Júlio de Mesquita Filho (UNESP) Instituto de Química Universidade Estatual Paulista Júlio de Mesquita Filho (UNESP)

Monolayers of molybdenum disulfide are of vital importance in the fabrication of optical and nanoelectronic devices. The development of thin and low-cost devices has increased the demand for synthe...

The development of near-infrared (NIR) photodetection technologies is driven by emerging applications such as medical imaging or optical sensors for electronic displays and machine vision. An all-organic upconverter (OUD) is a device that converts incident NIR light directly into visible light and consists of a monolithic stack of a NIR organic photodetector (OPD) and a visible organic light-emitting diode (OLED). We present OUDs that consist of NIR heptamethine cyanine dyes/C60 fullerene OPDs and a fluorescent tris(8-hydroxyquinolinato)aluminium (Alq3) OLED. The device metrics of performance are a high external quantum efficiency (EQE) of 43% of the OPD part and an OUD luminance turn-on at low bias voltages of 2 V. The dynamic response of the photocurrent and luminance is linear over a NIR light range corresponding to 26 dB. These OUDs upconvert NIR light at 830 nm to green light with a photon-to-photon conversion efficiency of 0.61%, close to the expected maximum.

Made available in DSpace on 2021-06-25T11:03:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-14 In this work, we synthesized colloidal silica nanospheres with an average size of 400 nm through the modified Stöber method and successfully fabricated an ordered close-packed silica nanosphere monolayer onto ITO-coated glass substrates using a three-step spin-coating method. ITO films showed resistivity comparable to that of commercial ITO and the silica nanosphere monolayer-coated ITO/glass substrate exhibited good optical transmittance in the visible (550 nm) and near-infrared (900 nm) regions of 62% and 82%, respectively. The results suggest that this monolayer can be used in optoelectronic devices to enhance efficiency in photovoltaic cells. Grupo de Nanociência e Nanotecnologia (NANO) Departamento de Física Universidade Federal de Juiz de Fora (UFJF) Laboratório de Biopolímeros e Biomateriais (BIOPOLMAT) Departamento de Biotecnologia Universidade de Araraquara (UNIARA) Departamento de Física Universidade Federal de Juiz de Fora (UFJF) Institudo de Química Universidade Estatual Paulista Julio de Mesquita Filho (UNESP) Laboratório de Optoeletrônica Molecular (LOEM) Departamento de Física Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) Faculdade de Ciências Farmacêuticas Universidade Estatual Paulista Julio de Mesquita Filho (UNESP) Institudo de Química Universidade Estatual Paulista Julio de Mesquita Filho (UNESP) Faculdade de Ciências Farmacêuticas Universidade Estatual Paulista Julio de Mesquita Filho (UNESP)

Made available in DSpace on 2021-06-25T11:03:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-13 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Instituto Nacional de Fotônica Bacterial nanocellulose (BNC) is a natural biopolymer obtained by gram-negative bacteria by means of a green and inexhaustible biotechnological process using glucose as producing source. BCN hydrogels is formed by cellulose nanofibrils that maintain an open network structure, an ideal matrix to produce new class of organic-inorganic nanocomposites (OIN) for multifunctional applications. The polyoxometalates (POMs) are complex molecules with several metallic ions sharing oxide ions, forming a highly symmetrical metal oxide cluster. Phosphotungstic acid (PWA), H3PW12O40 photoreduction process activated under ultraviolet irradiation, promoting color change. In this work, photochromic organic-inorganic nanocomposites were prepared by soaking phosphotungstic acid (H3PW12O40) in wet BNC membranes mats at room temperature. Semi-transparent and free-standing BNC/PWA nanocomposite with paper-like aspect were obtained. BNC network was able to control, stabilize and disperse PWA particles in a narrow nanometric distribution, and FTIR spectra indicated that the primary Keggin structure was also preserved in the nanocomposites, independently on the PWA content. The nanoparticles present a narrow distribution of around 16 nm, independently on the PWA concentration. BNC/PWA nanocomposites showed reversible photochromic behavior characteristic of the equilibrium between different tungsten oxidation states. PWA reduction (W6+→ W5+) and organic matrix oxidation is proposed to occur through a radical process involving the interaction of one electron from the oxygen atom of the PWA and one hydrogen from BNC matrix. The photochromic effect vanishes almost completely after 5 h. This mechanism is real in the presence of oxygen, however, if the membranes are left in nitrogen or under vacuum the blue color remains longer than 45 days. Photo-electrochemical behavior was studied by spectroelectrochemistry measurements. It is worth noting that all processes were still reversible in the timescale of the experiment and color changes were observed in several cycles. Institute of Chemistry São Paulo State University (UNESP) Laboratório de Biopolímeros e Biomateriais (BioPolMat) Universidade de Araraquara Instituto de Química – Universidade de São Paulo USP Departamento de Física Instituto de Ciências Exatas Universidade Federal de Juiz de Fora (UFJF) Deparment of Chemistry Federal University of São Departamento de Física Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) Institute of Chemistry São Paulo State University (UNESP) FAPESP: 2013/07793-6 FAPESP: 2013/24725-4 FAPESP: 2014/12424-2 FAPESP: 2016/11591-8 FAPESP: 2018/25512-8 FAPESP: 2020/04509-9 Instituto Nacional de Fotônica: 407822/2018-6

The growing interest in near-infrared (NIR) imaging is explained by the increasing number of applications in this spectral range, which includes process monitoring and medical imaging. NIR-to-visible optical upconverters made by integrating a NIR photosensitive unit with a visible emitting unit convert incident NIR light to visible light, allowing imaging of a NIR scene directly with the naked eye. Optical upconverters made entirely from organic and hybrid materials – which include colloidal quantum dots, and metal-halide perovskites – enable low-cost and pixel-free NIR imaging. These devices have emerged as a promising addition to current NIR imagers based on inorganic semiconductor photodiode arrays interconnected with read-out integrated circuitry. Here, we review the recent progress in the field of optical upconverters made from organic and hybrid materials, explain their functionality and characterization, and identify open challenges and opportunities., GRAPHICAL ABSTRACT 10.1080/14686996.2019.1610057-UF0001

Lanthanide organic complexes have high color purity with 100% theoretical internal quantum efficiency, making them good candidates for applications in organic light emitting devices. However, highly efficient and stable solution-processed devices based on terbium complexes have not been reported yet. Here, we present a solution-processed OLED using a novel terbium complex based on pyrazolone derivative ligand with pronounced efficiency. The device with co-host of 70% TcTa and 30% OXD-7 showed low turn-on voltage of 2.30 V, maximum current efficiency of 17.16 cd A−1 and external quantum efficiency of 7.15% at 1000 cd m−2. In addition, presenting a reduced roll-off efficiency compared to other reported terbium complex devices. This high efficiency for solution-processed Tb-based OLEDs clearly indicates the potential application of this Tb-complex in display applications.

The synthesis of metal nanoparticles (NPs) using microfluidic reactors has become a major method for limiting reagent consumption and achieve a precise control of the morphological properties. Failure in realizing the reproducibility of the results is mostly associated with the accumulation of metallic nanostructures on the walls of the microfluidic devices, periodically removed by acid treatment. In this study, we show that ns-pulsed laser ablation (PLA) in water can be a safe, effective, and green method for the regeneration of clogged microfluidic reactors. The effect of the laser-pulse fluence on the removal of metallic nanostructures was studied for the first time on silver (Ag) thin films with a thickness of 50 nm deposited over SiO2 substrates, using 3-mercaptopropyl trimethoxysilane as a chemical adhesion layer. As point of novelty, the experimental results show that at low fluence (F −2), ablation is principally caused by delamination of the thin film associated with the thermoelastic force while thermal processes inducing phase conversion of the metal dominate at higher fluence. Low-fluence regimes are better suited for the single-pulse removal of the nanomaterial, whereas in high F regimes, we observed melting and recondensation of the metal on the SiO2 surface so that multiple pulse interactions were necessary for complete ablation of the thin film. For the delamination and the phase transformation processes, the threshold fluences were 3.7 × 10−2 and 7.0 × 10−2 J cm−2, respectively. The experimental setup in the thermoelastic PLA regime was applied to unclog glass microfluidic devices used for synthesizing citrate-stabilized AgNPs. Using this simple and easily achievable laser-scanning experimental configuration, we demonstrated that PLA in water is a reliable and efficient technique, with results comparable to acidic treatment in terms of efficiency and time necessary for the complete removal of the Ag nanomaterial.

Organic light-emitting diode (OLED) devices in the archetype small-molecule fluorescent guest-host system tris(8-hydroxyquinolinato) aluminum ($\mathrm{Al}{\mathrm{q}}_{3}$) doped with 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran (DCM2) displays a redshift in light-emission frequency which is extremely sensitive to the dopant concentration. This effect can be used to tune the emission frequency in this particular class of OLEDs. In this work, a model is proposed to describe this effect using a combination of density functional theory quantum-chemical calculations and stochastic simulations of exciton diffusion via a F\"orster mechanism. The results show that the permanent dipole moments of the $\mathrm{Al}{\mathrm{q}}_{3}$ molecules generate random electric fields that are large enough to cause a nonlinear Stark shift in the band gap of neighboring DCM2 molecules. As a consequence of these nonlinear shifts, a non-Gaussian probability distribution of highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO-LUMO) gaps for the DCM2 molecules in the $\mathrm{Al}{\mathrm{q}}_{3}$ matrix is observed, with long exponential tails to the low-energy side. Surprisingly, this probability distribution of DCM2 HOMO-LUMO gaps is virtually independent of DCM2 concentration into the $\mathrm{Al}{\mathrm{q}}_{3}$ matrix, at least up to a fraction of 10%. This study shows that this distribution of gaps, combined with out-of-equilibrium exciton diffusion among DCM2 molecules, is sufficient to explain the experimentally observed emission redshift.

In this paper, a new method is presented for the magnetic characterization of nanoparticles that is especially suitable for samples with a low mass, on the order of tens of micrograms. We investigated the magnetic and morphological properties of the colloidal dispersions of iron oxide magnetic nanoparticles that were synthesized by two methods: chemical precipitation (co-precipitation) and pulsed laser ablation in liquid (PLA). We measured the stray field generated above the samples by scanning magnetic microscopy (SMM) and used a nonstandard model to obtain the magnetization of the nanoparticles. We assessed the performance of the method by comparing the magnetization curves with measurements obtained using commercial magnetometers. The errors in the saturation and remanent magnetization were found to be approximately ±0.18 Am2/kg and ±0.6 Am2/kg, respectively. As the samples exhibited a superparamagnetic state, we also used the magnetization curves to estimate the average size of the synthesized nanoparticles, which were found to be consistent with the results obtained using other techniques.

In this work is reported the fabrication and characterization of the triple-layer electroluminescent organic devices using a mixture of the gadolinium and europium β-diketonate complexes [GdxEuy(TTA)3 (TPPO)2] as emitting layer. The OLED devices contained the 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline aluminum) (Alq3) as electron transporting layer. The electroluminescence spectra present emission narrow bands from 5D1 → 7F1,2 and 5D0 → 7F0,1,2,3,4 transitions characteristics of the Eu3+ ion. These sharp lines are overlapped with a broad band attributed to the electrophosphorescence due to the T1 → S0 transition from TTA ligand. The intermolecular energy transfer from Gd-chelate to Eu-chelate is discussed based on this electrophosphorescence appearance.

The synthesis of a phenoxy-benzothiadiazole (BTD) derivative is reported for the first time. This derivative was employed as an intermediate in the obtention of two novel highly fluorescent aryl-phenoxy-BTD dyes. Their photophysical properties were evaluated in solution and the results indicate a strong intramolecular charge transfer (ICT) character in the excited state. The luminophore 3a, possessing a donor-BTD-phenoxide architecture, exhibits superior fluorescence quantum yield (0.67) than the designed acceptor-BTD-phenoxide dye (0.06). After electrochemical and photoluminescence characterization of thin films of 3a, an OLED with the configuration ITO/PEDOT:PSS/3a/TPBi/LiF/Al was constructed. This device displayed a green emission centered at 547 nm, with CIE coordinates of (0.40, 0.55). For comparison, an OLED using a previously reported luminescent BTD-pyridyl derivative was also constructed. The OLED made with the phenoxy-BTD derivative operated using less current density and led to higher irradiance and electrical stability, indicating the high potential of ArO-BTD dyes for future application in electroluminescent devices.

We report unusually high charge carrier mobilities for regioregular poly(3-hexyltiophene) (rrP3HT) in organic field-effect transistors (OFETs) using polyurethane (PU) as dielectric layer. Our devices display hole mobilities up to 1.37 cm2/V in the saturation regime and an ON/OFF current ratio higher than 103, operating at voltages as low as −10 V, with a high IDS current of 1.5 μA. We assign the measured high mobilities mainly to the low density of randomly-oriented electric dipoles at the semiconductor/dielectric interface, which leads to a narrow energy distribution of the electronic levels available for charge transport in rrP3HT. This is confirmed by experimental and theoretical techniques: (1) temperature-dependent transport measurements for extraction of disorder-induced distribution of electronic levels; (2) density functional theory (DFT) calculations of electric dipole moments of PU; and (3) liquid contact-angle measurements for the dipolar component of dielectric surface tension.

In recent years the use of solvent additives for fabrication of polymer-based solar cells has become an important procedure to induce morphological changes at the system nanoscale, a critical step to improve device performance. Yet the actual effects of those additives on the polymer’s backbone conformations (with coupled variations on the electronic structure) remain very elusive. By combining different experimental and theoretical techniques, we show that the use of the solvent additive 1,8-diiodooctane (DIO) might influence the conformation of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) chains resulting in improved properties of the film. We correlate this conformational variation with the photovoltaic response of F8T2:fullerene(C60) devices prepared using different DIO concentrations. We find that the efficiency of the devices increases more than 100%, and the hole mobility in the F8T2 films increases almost 1 order of magnitude with the use of DIO. A comparison between experimental da...

In this work, a near infrared (NIR) sensitive molecule, Tin(II)2,3-naphthalocyanine (SnNc) was characterized by different techniques. UV–Vis spectroscopy and cyclic voltammetry were performed in order to determine the absorption spectrum, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies of this molecule deposited in form of thin films. We found energies of 5.0 ± 0.1 eV and 3.7 ± 0.1 eV for HOMO and LUMO, respectively. The charge carrier mobility was also investigated by space charge limit current technique showing values of μh (8.8 ± 0.1) x 10−5 cm2V−1s−1. SnNc alone or blended with fullerene was used as efficient NIR sensitive layer due to its absorption around 875 nm. The crystalline structure of SnNc was studied by X-ray powder diffraction, showing a monoclinic system and P21/c space group, with cell parameters a = (15.948 ± 6) A, b = (15.818 ± 2) A, c = (14.649 ± 1) A and β = (67.096 ± 6) A. Desorption/Ionization-Time of Flight Mass Spectrometry (LDI-TOFMS) technique was employed to obtain information of molecular structure of the SnNc in thin film, showing that the thin film of the SnNc has no dimer formation. Due to its absorption around 875 nm, SnNc blended with fullerene was used as efficient NIR sensitive layer in the fabrication of an organic up-conversion device. When the device is submitted to IR radiation, a gain of about 133% was observed in the luminous efficiency when compared to values without IR irradiation.

In this work the synthesis, characterization and photoluminescent and electroluminescent behavior of the [Eu(DBM)₃(PTSO)₂] complex have been investigated. The emission spectrum of this Eu³⁺–β– diketonate complex show characteristics narrow bands arising from the ⁵D₀→⁷Fȷ (J = 0–4) transitions, which are split according to the selection rule for Cs, Cn or Cnv site symmetries. Triple and doublelayer organic light-emitting diodes (OLEDs) using NPB as hole transporting layer, Alq₃ as electron transporting layer and [Eu(DBM)₃(PTSO)₂] complex as emitting and electron transporting layer were grown and characterized. We found the presence of two concurrent mechanisms for the electroluminescent behavior: (1) the electroluminescence (EL) from the exciton-ligand-Eu³+ ion energy transfer, responsible for the EL narrow bands; and (2) the molecular electrophosphorescence with an initial energy transfer exciton-ligand and posterior intersystem crossing from the excited singlet S₁ to the triplet T state followed by molecular phosphorescence (T→S₀). The electroluminescent behavior of [Eu(DBM)₃(PTSO)₂] complex suggest that this complex is promising to applied at Light Conversion Molecular Devices (LCMDs) such as in OLED devices.

An in situ reaction of two optoelectronically active organic ligands (anionic thenoyltrifluoroacetylacetone, tta−, and neutral triphenylphosphine oxide, tppo) with erbium(III) ion in the presence of a base yielded a new erbium complex, [Er(tta)3(tppo)]. The solid and solution structure of the complex was established by X-ray crystallography, NMR, ESI-MS, FTIR, TGA and Raman spectroscopy. They indicate that the Er(III) ion is coordinated to seven oxygen atoms of three tta ligands and one tppo ligand in a monocapped octahedral geometry. The Judd–Ofelt parameters of the complex were determined by a least squares fitting and dealt with its chemical structure. On UV excitation through ligand mediation, the complex shows the characteristic near-infrared emission of the corresponding Er(III) ion at 1534 nm. Furthermore, a near infra-red organic light emitting diode (NIR-OLED) was fabricated with structure: ITO/[N,N′-bis(naphthalen-2-yl)-N,N′-bis(phenyl)benzidine]/[Er(tta)3(tppo)]/[2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)]/LiF/Al. This device, with maximum applied voltage of 23 V, shows a total quenching of visible emission and electroluminescence in the C-band region (1534 nm) which is suitable for third communication window applications in fiber optics. Finally, an organic diode was fabricated to determine charge carrier mobility of the complex using a steady-state method.

A series of NIR emitting novel ytterbium tris β-diketonate ternary complexes, [Yb(tta) 3 (L)]·H 2 O {tta = thenoyltrifluoroacetylacetone and L = dibenzyl sulphoxide (dbso), diphenyl sulphoxide (dpso) and benzoguinamine (bga)} was synthesised, and the photophysical and optoelectronic properties of their films were studied. Nuclear Magnetic Resonance (NMR) analysis indicates that the complexes are seven-coordinate which is a highly asymmetric structure enhancing the radiative transitions. It is an indicative of efficient energy transfer from coordinated ligands to Yb ion. The complexes were doped in Tris(4-carbazoyl-9-ylphenyl)amine (TcTa) organic matrix and the doped samples were used as the emitting layers to fabricate near-infrared organic light emitting diodes (NIR-OLEDs) with the structure: Indium tin oxide/{N,N′-bis(naphtalen-2-yl)-N,N′-bis(phenyl) benzidine} (25 nm)/[Yb-complexes] (10%): TcTa (40 nm)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline) (15 nm)/tris(8-hydroxy-quinolinato) aluminium (10 nm)/LiF (0.5 nm)/Al (120 nm). The complex, [Yb(tta) 3 (dpso)]·H 2 O shows the highest electroluminescence (EL) efficiency with maximum irradiance of 22.48 μW/cm 2 and current density of 29.5 mA/cm 2 at 15 V. It indicates an improved EL performance over the reported devices based on the Yb (III) complexes. In view of electrical characteristics, the current-voltage responses were interpreted by using Mott–Gurney model which allows us to determine the carrier mobility of the complexes.

A novel Er(III) β-diketonate complex, tris(dibenzoylmethanate)mono(triphenylphosphine oxide) erbium(III) or [Er(dbm)3(tppo)] was synthesised with dbm as a main sensitizer and tppo as a synergic ligand. The single crystal X-ray analysis reveals that the crystal structure of the complex is a triclinic centrosymmetric where Er(III) ion is coordinated to seven oxygen atoms; one O-atom from one tppo and six O-atoms from three dbm ligands. Shape-measure criterion measurements show that the complex possesses a distorted monocapped octahedron geometry, which facilitates the radiative transitions that is an indicative of efficient energy transfer from coordinated ligands to Er ion. The crystal structure is stabilised by the π–π stacking and CH/π interactions which lead to its high photo- and thermal stabilities. The complex was doped into a polymer matrix and the resulted material shows an enhanced luminescence intensity as well as full width at half maximum (fwhm) which allow its possible use for optical-amplification applications. Finally, a single layered organic diode was fabricated to determine charge carrier mobility (μ0) inside the complex. For this purpose, the Mott–Gurney model was used which gave sizable μ0 of 3.39 × 10−9 cm2/Vs (at

In this study, a novel type of tris(2-acyl-1,3-indandione)-aluminum(III) coordination compounds of the general formula [Al(acind)3]H2O, where 2-acyl-1,3-indandione (acind), 2-acetyl-1,3-indandione (aind), 2-benzoyl-1,3-indandione (bind), and 4-methyl-2-benzoyl-1,3-indandione (mbind), were synthesized and characterized by elemental analysis (CHN), Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H NMR) spectroscopies, thermal analysis (TG/DTG and DTA), and optical absorption spectroscopy in the UV-Vis region. These compounds present remarkably high green luminescence in powder and in thin-film forms. However, when these compounds are applied in glass/ITO/β-NPB/spiro-2CBP/[Al(acind)3]/Al and glass/ITO/β-NPB/[Al(acind)3]/LiF/Al electroluminescent devices, where spiro-2CBP is 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene and β-NPB is N,N’-bis(naphthalen-2-yl)-N,N’-bis(phenyl)-benzidine, the emission color tuned from green to red, reflecting a change from the direct charge recombination in the emitting layer of the [Al(acind)3] complexes to an exciplex-based emission in which [Al(acind)3] complexes and spiro 2-CBP acted as acceptor and donor, respectively. These results suggest that [Al(acind)3] complexes have potential applications as molecular light converter materials for fabricating new electroluminescent devices.

Made available in DSpace on 2020-12-12T02:23:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 A new biopolymer obtained from onion pulp (Allium cepa L.) was employed to produce a sustainable substrate for flexible organic light-emitting diodes (FOLEDs). Indium tin oxide (ITO) and SiO2 thin films were deposited by rf-magnetron sputtering onto these biosubstrates to obtain flexible, transparent, and conductive anodes, on top of which FOLEDs were produced. This new biomaterial exhibits an optical transparency of 63% at 550 nm. ITO films were optimized by varying rf power during deposition onto the biopolymers, and their electrical properties are comparable to the those of ITO grown on top of rigid substrates: a carrier concentration of -3.63 × 1021 cm-3 and carrier mobility of 7.72 cm2 V-1 s-1 for the optimized film. Consequently, the sheet resistance and resistivity of this ITO film were 8.92 ω sq-1 and 2.23 × 10-4 ω cm, respectively, hence allowing the production of FOLEDs. The A. cepa L. based FOLED was fabricated using CuPc, β-NPB, and Alq3 as organic layers, and it exhibited a maximum luminance of about 2062 cd m-2 at 16.6 V. The current efficiency reached a maximum value of 2.1 cd A-1 at 85.3 mA cm-2. The obtained results suggest the possibility to use these substrates for innovative biocompatible applications in optoelectronics, such as photodynamic therapy. Grupo de Nanociência e Nanotecnologia (NANO) Departamento de Física Universidade Federal de Juiz de Fora (UFJF) Laboratório de Biopolímeros e Biomateriais (BIOPOLMAT) Departamento de Química Universidade de Araraquara (UNIARA) Instituto de Física de São Carlos Universidade de São Paulo (USP) Instituto de Química Universidade Estatual Paulista Júlio de Mesquita Filho (UNESP) BioSmart Nanotechnology Laboratório de Optoeletrônica Molecular (LOEM) Departamento de Física Pontifícia Universidade Católica Do Rio de Janeiro (PUC-Rio) Departamento de Química Pontifícia Universidade Católica Do Rio de Janeiro (PUC-Rio) Instituto de Química Universidade Estatual Paulista Júlio de Mesquita Filho (UNESP)

Made available in DSpace on 2019-10-06T16:49:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-01-01 In this work, high transparent bacterial cellulose (HTBC) biocompatible membranes were produced to be used as substrates in organic light-emitting diodes (OLEDs). These multifunctional membranes are based on bacterial cellulose (BC) and an organic–inorganic sol, composed of boehmite (Boe) nanoparticles and epoxi modified siloxane (GTPS). In order to be used as substrates, BC/Boe-GPTS membranes were covered with silicon dioxide (SiO 2 ) and indium tin oxide (ITO) thin films deposited at room temperature using radio frequency (RF) magnetron sputtering. Visible light transmission improves to 88%, instead of 40% previously achieved. The electrical properties for HTBC/SiO 2 /ITO substrate shows that the ITO deposited films are n-type doped semiconductors with resistivity of 2.7 × 10 −4 Ω cm, carrier concentration of − 1.48 × 10 21 cm −3 , and mobility of 15.2 cm 2 V −1 s −1 . These values are comparable to those of commercial ITO deposited onto glass substrates. After the characterization of the HTBC film, we used it as a substrate for the fabrication of a small molecule organic light-emitting diode OLED. The maximum efficiencies obtained were 1.95 cd/A and 1.68 cd/A for the reference OLED and the HTBC OLED, respectively. The HTBC OLED efficiency is then around 86% of the standard ITO-based OLED. This is clearly a good improvement, since previous BC-based simple architecture devices without Boe-GPTS have an efficiency 50% smaller than that of the standard OLED. Laboratório de Eletrônica Orgânica Departamento de Física Universidade Federal de Juiz de Fora UFJF Divisão de Metrologia de Materiais (DIMAT) Inmetro Laboratório de Biopolímeros e Biomateriais – BioPolMat Universidade de Araraquara (Uniara) Departamento de Química Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Universidade de São Paulo Instituto de Química Universidade Estadual Paulista UNESP Laboratório de Optoeletrônica Molecular Departamento de Física Pontifícia Universidade Católica do Rio de Janeiro PUC-Rio Instituto de Química Universidade Estadual Paulista UNESP

In this work, the meso-tetra[4-(2-(3-n-pentadecylphenoxy)ethoxy]phenylporphyrin (H2P), obtained from the cashew nut shell liquid (CNSL), and its zinc (ZnP) and copper (CuP) metallic complexes, were applied as emitting layers in organic light emitting diodes (OLEDs). These compounds were characterized via optical and electrochemical analysis and the electroluminescent properties of the device have been studied. We performed a cyclic voltammetry analysis to determine the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels for the porphyrins, in order to select the proper materials to assemble the device. H2P and ZnP presented fluorescence emission band in the red region, from 601 nm to 718 nm. Moreover, we verified that the introduction of bulky substituents hinders the &pi, &ndash, &pi, stacking, favoring the emission in the film. In addition, the strongest emitter, ZnP, presented a threshold voltage of 4 V and the maximum irradiance of 10 &mu, W cm&minus, 2 with a current density (J) of 15 mA cm&minus, 2 at 10 V. The CuP complex showed to be a favorable material for the design of OLEDs in the infrared. These results suggest that the porphyrins derived from a renewable source, such as CNSL, is a promising material to be used in organic optoelectronic devices such as OLEDs.

Made available in DSpace on 2021-06-25T11:03:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Bacterial cellulose (BC) is a biocompatible and nontoxic biopolymer that has been successfully used as a substrate for flexible organic light emitting diodes (OLEDs). Although BC membranes exhibit excellent mechanical properties and industrial scalability, they are semitransparent, which limits their performance. To improve the optical properties of BC membranes, methods such as the polymerization of different inorganic–organic hybrid materials and petrochemical derivative monomers have been considered; however, these methods require considerable time and effort. In this work, transparent BC membranes for conformable OLEDs substrates are fabricated by spray coating a solution of recycled petrochemical plastics, found in expanded foam package wastes, and d-limonene, which is a green solvent extracted from orange peels. This fabrication approach is highly scalable and can be considered a sustainable technique to develop high performance transparent substrates for photonic applications based on both recovered petrochemical polymers and naturally occurring biopolymers. In terms of the morphological and structural properties, the resulting transparent membranes exhibit a lower roughness than pristine BC. The resulting BC-PS composite is used as a substrate for OLED fabrication. The conformable OLEDs exhibit a current efficiency of up to 5 cd A−1 (16 000 cd m−2) and power density of ≈2.8 mW cm−2. Institute of Chemistry São Paulo State University – Unesp Departamento de Física Pontifícia Universidade Católica do Rio de Janeiro Grupo de Pesquisa em Biopolímeros e Biomateriais (BioPolMat) University of Araraquara (UNIARA) Department of Chemistry and Chemical Engineering Chalmers University of Technology Laboratório de Eletrônica Orgânica Departamento de Física Universidade Federal de Juiz de Fora UFJF Institute of Chemistry São Paulo State University – Unesp

A low symmetry NIR emitting ytterbium (III) β-diketonate ternary complex with composition, [Yb(tta)3(tppo)]·H2O (tta = thenoyltrifluoroacetylacetone and tppo = triphenyl phosphine oxide) was synthesized and fully characterized. Single crystal X-ray analysis and shape measurement calculations indicate that the complex is a seven-coordinate and possesses distorted trigonal prism geometry with coordination polyhedra YbO7 where the Yb(III) ion is surrounded by seven oxygen atoms of three tta and one tppo ligands. It is a highly asymmetric structure enhancing the radiative transitions which is an indicative of efficient energy transfer from coordinated ligands to Yb ion. The complex was doped in a tris(4-carbazoyl-9-ylphenyl)amine (TcTa) matrix and used as an emitting layer to fabricate near-infrared organic light emitting device (NIR-OLED) with the structure: ITO/{N,N′-bis(naphtalen-2-yl)-N,N′-bis(phenyl) benzidine} (25 nm)/[Yb-complex] (10%): TcTa (40 nm)/BCP (15 nm)/Alq3 (10 nm)/LiF (0.5 nm)/Al (120 nm). The complex based NIR-OLED showed good EL efficiency with maximum irradiance of 19.29 μW/cm2 and current density of 27.3 mA/cm2 at 15 V. In view of electrical characteristics, the charge carrier mobility, μ0, of the complex was determined by using Mott–Gurney model which gave a sizable value of 4.50 × 10−8 cm2/Vs.

Hydrazones constitute a class of compounds presenting azomethine R′R″N N CH R hydrogens, which show diverse properties and a wide range of applications. A hydrazone derived from the antituberculosis drug isoniazid, namely, N,N′-diisonicotinoyl-2-hydroxy-5-methylisophthalaldehyde hydrazone (DMD) was synthesized and chemically characterized. Its luminescent properties were also investigated, as well as the possibility of using this compound as a constituent of the emitting layer for the fabrication of OLEDs. Co-deposited devices were fabricated using the organic molecule BSBF as matrix and DMD as dopant. All the devices presented a broad electroluminescence band, in which it was possible to recognize the DMD emission along with emissions of some of the other organic layers. The best results were obtained with 35% DMD doping, achieving a luminance of about 35 cd/m2.

Organic light-emitting diodes using phosphorescent dyes (PHOLEDs) have excellent performance, with internal quantum efficiencies approaching 100%. To maximize their performance, PHOLED devices use a conductive organic host material with a sufficiently dispersed phosphorescent guest to avoid concentration quenching. Fac-tris(2-phenylpyridine) iridium, [Ir(ppy)3] is one of the most widely used green phosphorescent organic compounds. In this work, we used scanning transmission electron microscopy (STEM) equipped with HAADF (high-angle annular dark-field) and EDS (energy dispersive X-ray spectroscopy) detectors to analyze the distribution of the [Ir(ppy)3] concentration in the host material. This analysis technique, employed for the first time in co-deposited organic thin films, can simultaneously obtain an image and its respective chemical information, allowing for definitive characterization of the distribution and morphology of [Ir(ppy)3]. The technique was also used to analyze the effect of the vibration of the substrate during thermal co-deposition of the [Ir(ppy)3] molecules into an organic matrix.

In this study, we investigated the effects generated by ion bombardment on the charge transport properties of organic semiconductor devices. Focused ion beam (FIB) technology was used to induce the bombardment at different ion doses on poly(3-hexylthiophene) (rrP3HT) and poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) organic semiconductors. The characterization techniques demonstrated the presence of two regimes: at 2E13 and 2E14 doses. UV–Vis absorption, Raman spectroscopy and advanced electron microscopy analysis reveal the presence of a chemically and structurally modified layer approximately 40 nm thick. The results were confirmed by theoretical ion tracking simulation nearly 40–50 nm thick from the organic surface. The dependence of charge transport and ion bombardment was clearly evidenced by modifications in the charge carrier mobility that formed defects induced by the ion beams, such as degassing, cross-linking polymer chains, and the transformation of functional groups in the ion tracking region.

A series of luminescent aryloxy-benzothiadiazole derivatives with architectures ArO-BTD-Ar’ and ArO-BTD-NAr’ were synthetized. The aim was to achieve a molecular design based on restriction of intramolecular rotation of the ArO- group associated to the presence of bulky aryl or N-aryl groups, which can avoid detrimental π-π stacking and favor radiative decays in the aggregated/solid state. In solution, these compounds showed fluorescence emission located in the blue to red regions with relative high fluorescence quantum yields (φFL = 0.27–0.74). For all ArO-BTD-Ar’ derivatives, emission enhancement was observed upon aggregation. The essential role of the ArO- group in the AIEEgenic ability was confirmed by comparing with Ar’-BTD-Ar’ analogs. Some solid ArO-BTD-Ar’ compounds displayed higher φFL than when in solution. Their aggregation-induced enhanced emission (AIEE) were corroborated by studies in water/acetone systems (I/I0 emission rations up to 7.7). Monocrystal X-ray analysis of selected compounds confirmed the twisted nature and absence of detrimental π-π stacking. The more emissive compound (φFL = 0.83) was applied as emitting material in a green OLED structure, presenting turn-on voltage around 3.5 V and luminance up to 1200 cd m−2, with a maximum current efficiency of 5.6 × 10−1 cd A−1 at 6.5 V.

Here we report the effect of an additive solvent, the 1,8-diiodooctane (DIO) on the performance of a bilayer organic photovoltaic (OPV) device which active layer comprises the poly[2,7-(9,9-bis(2 ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) as the electron donor material and C60 as the electron acceptor material. We observed that when the donor layer was treated with 1% of DIO the power conversion efficiency (PCE) of the device increase 138.4% in relation to the device with a non-treated donor layer and 21.3% in relation to the device containing a donor layer submitted to a thermal annealed. The main effects that lead to this increase in PCE are the large interfacial area between donor and acceptor materials and the improved conductivity at low voltages. The increase in polymer surface roughness leads to a more effective PSiF-DBT/C60 interface for exciton dissociation. This effect, as well as the increase in the conductivity, raised the short circuit current density (JSC) to 13.89 mA/cm2 and PCE to 4.84%. Our conclusions are supported by morphological analysis, chemical cross-sectional evaluations with advanced microscopy techniques, charge mobility measurements as well as by theoretical simulations of the devices in which the changes on the donor/acceptor interfacial area were considered. The outcomes suggests that, solvent additives could be an alternative treatment to replace the thermal annealing which imposes further difficulties to perform the lab-to-manufacturing upscaling.

In this work, we perform morphological and physicochemical studies of Dactylopius opuntiae (cochineal) with electron microscopy and explore their use as a transporting layer for organic electronic devices. The charge transport properties of this pigment were investigated through current-voltage measurements. The current-voltage characteristics have shown that the cochineal can be used as a hole-transporting layer (HTL) with mobility of 5.30 ± 0.03 × 10−4cm2V−1 s−1. Different analyses were realized on this pigment and the results were compared with other HTL organic compounds, as Poly(3,4-ethylene dioxy thiophene): poly(styrene sulfonate) (PEDOT:PSS). The results show that the cochineal pigment does not produce luminescence and has a band gap of 2.6 ± 0.2 eV with optical absorption in the visible range. The roughness of cochineal thin films was measured after filtering the solution with a value of 11.8 ± 0.2 nm. Cochineal and PEDOT:PSS were successfully used as HTL in the fabrication of a [Ir(fliq)2acac] based PHOLED. The results show an increase in the electroluminescent color purity emission due to the filtering action of the natural pigment when compared with the PEDOT:PSS based in this device.

The degradation processes of tris(8-hydroxyquinoline) (Alq3) and tris(dibenzoylmethane) mono(1,10-phenanthroline)europium(III) (Eu(dbm)3(phen)) thin films are investigated by the use of AFM, photoluminescence and SPR spectroscopy. The plasmonic sensors are operated both in air and nitrogen environments, where they are irradiated with controlled doses of UVA radiation. AFM results don’t reveal the formation of heterogeneous phases and crystallization under air exposure. The organic thin films change their refractive index under both types of exposure and act as a protective layer against oxidation for the SiO2/MPTS/metal interface of the plasmonic sensors. SPR measurements reveal a strict correlation between the refractive index increase and quenching of the photoluminescence of the organic thin films. The results are promising for the development of compact plasmonic UVA dosimeters in the surface plasmon coupled emission configuration (SPCE) with lanthanide β-diketonate complex materials (patent pending).