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1.
Chirality ; 35(5): 270-280, 2023 May.
Artículo en Inglés | MEDLINE | ID: mdl-36847610

RESUMEN

Luminescent lanthanide complexes exhibiting chiroptical properties are attracting attention for their application in chiral optoelectronics and photonics, thanks to their unique optical properties, allied to intraconfigurational f-f transitions, which are generally electric-dipole-forbidden and can be magnetic dipole-allowed, which in an appropriate environment can lead to high dissymmetry factors and strong luminescence, in the presence of an antenna ligand. However, because luminescence and chiroptical activity are governed by different selection rules, their successful application in commonly used technologies is still an expectation. Recently, we showed that europium complexes bearing ß-diketonates acting as luminescence sensitizers, and chiral bis(oxazolinyl) pyridine derivatives as the chirality inducer, reasonably perform in circularly polarized (CP) organic light-emitting devices (OLEDs). Indeed, europium ß-diketonate complexes are an interesting molecular starting point, given their strong luminescence and their established use in conventional (i.e., nonpolarized) OLEDs. In this context, it is interesting to investigate in detail the impact of the ancillary chiral ligand on complex emission properties and the performances of corresponding CP-OLEDs. Here we show that, by incorporating the chiral compound as emitter in the architecture of solution processed electroluminescent devices, CP emission is retained, and the efficiency of the device is comparable to reference unpolarized OLED. The observed remarkable dissymmetry values strengthen the position of chiral lanthanide-OLEDs as CP-emitting devices.

2.
Molecules ; 28(1)2022 Dec 22.
Artículo en Inglés | MEDLINE | ID: mdl-36615268

RESUMEN

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.


Asunto(s)
Grafito , Puntos Cuánticos , Carbono/química , Nitrógeno/química , Puntos Cuánticos/química , Análisis Espectral , Oxidación-Reducción
3.
Development ; 143(4): 658-69, 2016 Feb 15.
Artículo en Inglés | MEDLINE | ID: mdl-26884398

RESUMEN

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disorder characterized by muscle wasting and premature death. The defective gene is dystrophin, a structural protein, absence of which causes membrane fragility and myofiber necrosis. Several lines of evidence showed that in adult DMD patients dystrophin is involved in signaling pathways that regulate calcium homeostasis and differentiation programs. However, secondary aspects of the disease, such as inflammation and fibrosis development, might represent a bias in the analysis. Because fetal muscle is not influenced by gravity and does not suffer from mechanical load and/or inflammation, we investigated 12-week-old fetal DMD skeletal muscles, highlighting for the first time early alterations in signaling pathways mediated by the absence of dystrophin itself. We found that PLC/IP3/IP3R/Ryr1/Ca(2+) signaling is widely active in fetal DMD skeletal muscles and, through the calcium-dependent PKCα protein, exerts a fundamental regulatory role in delaying myogenesis and in myofiber commitment. These data provide new insights into the origin of DMD pathology during muscle development.


Asunto(s)
Señalización del Calcio , Feto/metabolismo , Inositol 1,4,5-Trifosfato/metabolismo , Desarrollo de Músculos , Músculo Esquelético/embriología , Distrofia Muscular de Duchenne/embriología , Distrofia Muscular de Duchenne/metabolismo , Animales , Biomarcadores/metabolismo , Biopsia , Calcio/metabolismo , Canales de Calcio/metabolismo , Feto/patología , Regulación del Desarrollo de la Expresión Génica , Ratones Endogámicos C57BL , Ratones Endogámicos mdx , Modelos Biológicos , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/patología , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Distrofia Muscular Animal/metabolismo , Distrofia Muscular Animal/patología , Distrofia Muscular de Duchenne/patología , Factor de Transcripción PAX7/metabolismo , Proteína Quinasa C-alfa/metabolismo
4.
Nano Lett ; 18(6): 3441-3448, 2018 06 13.
Artículo en Inglés | MEDLINE | ID: mdl-29722262

RESUMEN

Colloidal nanoplatelets (NPLs), owing to their efficient and narrow-band luminescence, are considered as promising candidates for solution-processable light-emitting diodes (LEDs) with ultrahigh color purity. To date, however, the record efficiencies of NPL-LEDs are significantly lower than those of more-investigated devices based on spherical nanocrystals. This is particularly true for red-emitting NPL-LEDs, the best-reported external quantum efficiency (EQE) of which is limited to 0.63% (EQE = 5% for green NPL-LEDs). Here, we address this issue by introducing a charge-regulating layer of a polar and polyelectrolytic polymer specifically engineered with complementary trimethylammonium and phosphonate functionalities that provide high solubility in orthogonal polar media with respect to the NPL active layer, compatibility with the metal cathode, and the ability to control electron injection through the formation of a polarized interface under bias. Through this synergic approach, we achieve EQE = 5.73% at 658 nm (color saturation 98%) in completely solution processed LEDs. Remarkably, exposure to air increases the EQE to 8.39%, exceeding the best reports of red NPL-LEDs by over 1 order of magnitude and setting a new global record for quantum-dot LEDs of any color embedding solution-deposited organic interlayers. Considering the emission quantum yield of the NPLs (40 ± 5%), this value corresponds to a near-unity internal quantum efficiency. Notably, our devices show exceptional operational stability for over 5 h of continuous drive in air with no encapsulation, thus confirming the potential of NPLs for efficient, high-stability, saturated LEDs.

5.
Chemphyschem ; 18(16): 2157-2161, 2017 Aug 18.
Artículo en Inglés | MEDLINE | ID: mdl-28240411

RESUMEN

A novel and versatile approach to tune photoluminescence and electroluminescence by in situ controlled thermal deprotonation is presented. This methodology, based on a single organic π-conjugated material (pyrene derivative), allows the manufacturing of organic light-emitting diode (OLED) prototypes by solution methods with controlled tunable emission ranging from the orange (protonated form of the dye) to the blue (pristine or deprotonated form). While several protonation/deprotonation cycles can be performed on thin films, for the devices only one cycle is possible so that their use as anti-fraud labels can be envisaged. OLEDs exhibit daylight visible brightness of 150 cd m-2 and device lifetime exceeding 30 hours of continuous operation. Thanks to the simplicity of both material design and device fabrication our approach opens new perspectives in the wide field of thermal sensors for customer care or risk perception.

6.
Inorg Chem ; 56(9): 4829-4839, 2017 May 01.
Artículo en Inglés | MEDLINE | ID: mdl-28387513

RESUMEN

New heteroleptic compounds of platinum(II)-containing cyclometalated N-heterocyclic carbenes, [PtCl(R-C^C*)(PPh3)] [R-CH^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene (R-C = Naph; 1A), 1-[4-(ethoxycarbonyl)phenyl]-3-methyl-1H-imidazol-2-ylidene (R = CO2Et; 1B), and [Pt(R-C^C*)(py)(PPh3)]PF6 (py = pyridine; R-C = Naph, 2A; R = CO2Et, 2B], have been prepared and fully characterized. All of them were obtained as the trans-(C*,PPh3) isomer in high yields. The selectivity of their synthesis has been explained in terms of the degree of transphobia (T) of pairs of ligands in trans positions. X-ray diffraction studies on both 2A and 2B revealed that only in 2A, containing a C^C* with a more extended π system, do the molecules assemble themselves into head-to-tail pairs through intermolecular π···π contacts. The photophysical properties of 2A and 2B and those of the related compounds [Pt(NC-C^C*)(PPh3)L]PF6 [NC-CH^C*-κC* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene; L = pyridine (py; 2C), 2,6-dimethylphenylisocyanide (CNXyl; 3C), and 2-mercapto-1-methylimidazole (MMI; 4C)] have been examined to analyze the influence of the R substituent on R-C^C* (R-C = Naph; R = CO2Et, CN) and that of the ancillary ligands (L) on them. Experimental data and time-dependent density functional theory calculations showed the similarity of the electronic features associated with R-C^C* (R = CN, CO2Et) and their difference with respect to R-C^C* (R-C = Naph). All of the compounds are very efficient blue emitters in poly(methyl methacrylate) films under an argon atmosphere, with QY values ranging from 68% (2B) to 93% (2C). In the solid state, the color of the emission changes to yellowish-orange for compounds 2A (λmax = 600 nm) and 3C (λmax = 590 nm) because of the formation of aggregates through intermolecular π···π interactions. 2C and 3C were chosen to fabricate fully solution-processed electroluminescent devices with blue-light (2C), yellow-orange-light (3C), and white-light (mixtures of 2C and 3C) emission from neat films of the compounds as emitting layers.

7.
Inorg Chem ; 55(17): 8527-42, 2016 Sep 06.
Artículo en Inglés | MEDLINE | ID: mdl-27494635

RESUMEN

The heterofunctional and rigid ligand N,N'-diphosphanyl-imidazol-2-ylidene (PCNHCP; P = P(t-Bu)2), through its phosphorus and two N-heterocyclic carbene (NHC) donors, stabilizes trinuclear chain complexes, with either Au3 or AgAu2 cores, and dinuclear Au2 complexes. The two oppositely situated PCNHCP (L) ligands that "sandwich" the metal chain can support linear and rigid structures, as found in the known tricationic Au(I) complex [Au3(µ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 (OTf = CF3SO3; [Au3L2](OTf)3; Chem. Commun. 2014, 50, 103-105) now also obtained by transmetalation from [Ag3(µ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 ([Ag3L2](OTf)3), or in the mixed-metal tricationic [Au2Ag(µ3-PCNHCP,κP,κCNHC,κP)2](OTf)3 ([Au2AgL2](OTf)3). The latter was obtained stepwise by the addition of AgOTf to the digold(I) complex [Au2(µ2-PCNHCP,κP,κCNHC)2](OTf)2 ([Au2L2](OTf)2). The latter contains two dangling P donors and displays fluxional behavior in solution, and the Au···Au separation of 2.8320(6) Å in the solid state is consistent with metallophilic interactions. In the solvento complex [Au3Cl2(tht)(µ3-PCNHCP,κP,κCNHC,κP)](OTf)·MeCN ([Au3Cl2(tht)L](OTf)·MeCN), which contains only one L and one tht ligand (tht = tetrahydrothiophene), the metal chain is bent (148.94(2)°), and the longer Au···Au separation (2.9710(4) Å) is in line with relaxation of the rigidity due to a more "open" structure. Similar features were observed in [Au3Cl2(SMe2)L](OTf)·2MeCN. A detailed study of the emission properties of [Au3L2](OTf)3, [Au3Cl2(tht)L](OTf)·MeCN, [Au2L2](OTf)2, and [Au2AgL2](OTf)3 was performed by means of steady state and time-resolved photophysical techniques. The complex [Au3L2](OTf)3 displays a bright (photoluminescence quantum yield = 80%) and narrow emission band centered at 446 nm with a relatively small Stokes' shift and long-lived excited-state lifetime on the microsecond timescale, both in solution and in the solid state. In line with the very narrow emission profile centered in the violet-blue region, fabrication of organic light-emitting devices (OLEDs) comprising the [Au3L2](OTf)3 complex demonstrated its usefulness as a deep-blue emitter in solution-processed OLEDs. Electrochemical and Raman spectroscopic studies were also performed on [Au3L2](OTf)3. Experimental results were rationalized by means of Wave-Function Theory (WFT) and Density Functional Theory (DFT). MP2 calculations gave a satisfactory description of the structures of the cationic complexes [Au3L2](3+) and [Au2L2](2+) and pointed to Au···Au interactions having an electrostatic component owing to the dissimilar charge distribution in the chain caused by the heterofunctional ligand. The nature of the emitting states and their geometric distortions relative to the ground states in [Au3L2](3+) and [Au2L2](2+) was studied by DFT, revealing contraction of the Au···Au distances and coordination geometry changes by association of the dangling P donor, respectively.

8.
Nano Lett ; 15(8): 5455-64, 2015 Aug 12.
Artículo en Inglés | MEDLINE | ID: mdl-26198761

RESUMEN

Colloidal quantum dots (QDs) are emerging as true candidates for light-emitting diodes with ultrasaturated colors. Here, we combine CdSe/CdS dot-in-rod heterostructures and polar/polyelectrolytic conjugated polymers to demonstrate the first example of fully solution-based quantum dot light-emitting diodes (QD-LEDs) incorporating all-organic injection/transport layers with high brightness, very limited roll-off and external quantum efficiency as high as 6.1%, which is 20 times higher than the record QD-LEDs with all-solution-processed organic interlayers and exceeds by over 200% QD-LEDs embedding vacuum-deposited organic molecules.

9.
Angew Chem Int Ed Engl ; 55(8): 2714-8, 2016 Feb 18.
Artículo en Inglés | MEDLINE | ID: mdl-26804423

RESUMEN

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.

10.
Nano Lett ; 14(2): 486-94, 2014 Feb 12.
Artículo en Inglés | MEDLINE | ID: mdl-24328946

RESUMEN

The emission color from colloidal semiconductor nanocrystals (NCs) is usually tuned through control of particle size, while multicolor emission is obtained by mixing NCs of different sizes within an emissive layer. Here, we demonstrate that recently introduced "dot-in-bulk" (DiB) nanocrystals can emit two-color light under both optical excitation and electrical injection. We show that the effective emission color can be controlled by adjusting the relative amplitudes of the core and shell emission bands via the intensity of optical excitation or applied bias in the cases of photoluminescence (PL) and electroluminescence (EL), respectively. To investigate the role of nonradiative carrier losses due to trapping at intragap states, we incorporate DiB NCs into functional light-emitting diodes and study their PL as a function of applied bias below the EL excitation threshold. We show that voltage-dependent changes in core and shell emissions are not due to the applied electric field but rather arise from the transfer of charges between the anode and the NC intragap trap sites. The changes in the occupancy of trap states can be described in terms of the raising (lowering) of the Fermi level for reverse (direct) bias. We find that the applied voltage affects the overall PL intensity primarily via the electron-trapping channel while bias-induced changes in hole-trapping play a less significant role, limited to a weak effect on core emission.

11.
Biomacromolecules ; 14(10): 3549-56, 2013 Oct 14.
Artículo en Inglés | MEDLINE | ID: mdl-24032431

RESUMEN

New strategies are requested for the preparation of bioinspired host-guest complexes to be employed in technologically relevant applications, as sensors and optoelectronic devices. We report here a new approach employing a single monomeric protein as host for the strongly fluorescent rhodamine dye. The selected protein, belonging to the intracellular lipid binding protein family, fully encapsulates one rhodamine molecule inside its cavity forming a host-guest complex stabilized by H and π-hydrogen bonds, a salt bridge, and favorable hydrophobic contacts, as revealed by the NMR derived structural model. The protein-dye solutions are easily processable and form homogeneous thin films exhibiting excellent photophysical and morphological properties, as derived from photoluminescence and AFM data. The obtained results represent the proof of concept of the viability of this bio host-guest system for the development of bioinspired optoelectronic devices.


Asunto(s)
Proteínas Portadoras/química , Colorantes Fluorescentes/química , Glicoproteínas de Membrana/química , Rodaminas/química , Agua/química , Enlace de Hidrógeno , Interacciones Hidrofóbicas e Hidrofílicas , Mediciones Luminiscentes , Ensayo de Materiales , Microscopía de Fuerza Atómica , Modelos Moleculares , Estructura Molecular
12.
Biochim Biophys Acta Gen Subj ; 1867(1): 130253, 2023 01.
Artículo en Inglés | MEDLINE | ID: mdl-36228877

RESUMEN

BACKGROUND: Cells exposed to stress factors experience time-dependent variations of metabolite concentration, acting as reliable sensors of the effective concentration of drugs in solution. NMR can detect and quantify changes in metabolite concentration, thus providing an indirect estimate of drug concentration. The quantification of bactericidal molecules released from antimicrobial-treated biomedical materials is crucial to determine their biocompatibility and the potential onset of drug resistance. METHODS: Real-time NMR measurements of extracellular metabolites produced by bacteria grown in the presence of known concentrations of an antibacterial molecule (irgasan) are employed to quantify the bactericidal molecule released from antimicrobial-treated biomedical devices. Viability tests assess their activity against E. coli and S. aureus planktonic and sessile cells. AFM and contact angle measurements assisted in the determination of the mechanism of antibacterial action. RESULTS: NMR-derived concentration kinetics of metabolites produced by bacteria grown in contact with functionalized materials allows for indirectly evaluating the effective concentration of toxic substances released from the device, lowering the detection limit to the nanomolar range. NMR, AFM and contact angle measurements support a surface-killing mechanism of action against bacteria. CONCLUSIONS: The NMR based approach provides a reliable tool to estimate bactericidal molecule release from antimicrobial materials. GENERAL SIGNIFICANCE: The novelty of the proposed NMR-based strategy is that it i) exploits bacteria as sensors of the presence of bactericidal molecules in solution; ii) is independent of the chemo-physical properties of the analyte; iii) establishes the detection limit to nanomolar concentrations.


Asunto(s)
Antiinfecciosos , Staphylococcus aureus , Escherichia coli , Antibacterianos/farmacología , Antibacterianos/química , Bacterias , Antiinfecciosos/farmacología
13.
Phys Chem Chem Phys ; 14(39): 13646-50, 2012 Oct 21.
Artículo en Inglés | MEDLINE | ID: mdl-22964896

RESUMEN

In a smart solution-processable luminescent poly(norbornene)/oxazine-1 (Ox1) intercalated fluoromica nanohybrid, the supramolecular organization of the Ox1 dyes can be tuned at the nanoscale level and a deep red emission band switched on by inducing a phase segregation of aligned molecules within the fluoromica layered scaffold. By combining low-temperature photoluminescence and ultrafast pump-probe spectroscopy we prove that the nanoconstrained Ox1 molecules are organized in a J-type packing and we highlight the critical factor that controls such a supramolecular dye arrangement.


Asunto(s)
Colorantes Fluorescentes/química , Nanoestructuras/química , Oxazinas/química , Plásticos/química , Luminiscencia , Soluciones , Análisis Espectral , Temperatura
14.
Inorg Chem ; 50(12): 5417-29, 2011 Jun 20.
Artículo en Inglés | MEDLINE | ID: mdl-21615131

RESUMEN

The synthesis and the molecular and photophysical characterization, together with solid state and solution structure analysis, of a series of europium complexes based on ß-diketonate ligands are reported. The Eu(III) complex emission, specifically its photoluminescence quantum yield (PL-QY), can be tuned by changing ligands which finely modifies the environment of the metal ion. Steady-state and time-resolved emission spectroscopy and overall PL-QY measurements are reported and related to geometrical features observed in crystal structures of some selected compounds. Moreover, paramagnetic NMR, based on the analogous complexes with other lanthanides, are use to demonstrate that there is a significant structural reorganization upon dissolution, which justifies the observed differences in the emission properties between solid and solution states. The energy of the triplet levels of the ligands and the occurrence of nonradiative deactivation processes clearly account for the luminescence efficiencies of the complexes in the series.


Asunto(s)
Europio/química , Cetonas/química , Compuestos Organometálicos/química , Teoría Cuántica , Tiofenos/química , Ligandos , Luminiscencia , Estructura Molecular , Compuestos Organometálicos/síntesis química
15.
Dalton Trans ; 50(26): 9208-9214, 2021 Jul 06.
Artículo en Inglés | MEDLINE | ID: mdl-34125122

RESUMEN

Colloidal semiconductor nanoplatelets (NPLs) are a subgroup of quantum confined materials that have recently emerged as promising active materials for solution processed light-emitting diodes (LEDs) thanks to their peculiar structural and electronic properties as well as their reduced dimensionality. Nowadays, the conventional structure for NPL-based LEDs makes use of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a hole transporting layer (HTL). This is a well-known conjugated conductive polymer because it leads to high LED efficiency, though it has limited stability in air due to its intrinsic acidity and hygroscopicity. Here, we develop a nanocomposite aqueous ink, obtained by blending commercial PEDOT:PSS with water-based, stable and highly concentrated molybdenum disulfide (MoS2) nanosheets, obtained via liquid phase exfoliation (LPE), which is suitable as a HTL for solution processed NPL-based LEDs. We demonstrate that the MoS2 additive effectively works as a performance booster in unpackaged devices, thereby prolonging the lifetime up to 1000 hours under ambient conditions. Moreover, the addition of MoS2 induces a modification of the anode interface properties, including a change in the work function and a significant enhancement of the permittivity of the HTL.

16.
Nanomaterials (Basel) ; 12(1)2021 Dec 29.
Artículo en Inglés | MEDLINE | ID: mdl-35010034

RESUMEN

The use of water-processable nanoparticles (WPNPs) is an emerging strategy for the processing of organic semiconducting materials into aqueous medium, dramatically reducing the use of chlorinated solvents and enabling the control of the nanomorphology in OPV active layers. We studied amphiphilic rod-coil block copolymers (BCPs) with a different chemical structure and length of the hydrophilic coil blocks. Using the BCPs blended with a fullerene acceptor material, we fabricated NP-OPV devices with a sustainable approach. The goal of this work is to clarify how the morphology of the nanodomains of the two active materials is addressed by the hydrophilic coil molecular structures, and in turn how the design of the materials affects the device performances. Exploiting a peculiar application of TEM, EFTEM microscopy on WPNPs, with the contribution of AFM and spectroscopic techniques, we correlate the coil structure with the device performances, demonstrating the pivotal influence of the chemical design over material properties. BCP5, bearing a coil block of five repeating units of 4-vinilpyridine (4VP), leads to working devices with efficiency comparable to the solution-processed ones for the multiple PCBM-rich cores morphology displayed by the blend WPNPs. Otherwise, BCP2 and BCP15, with 2 and 15 repeating units of 4VP, respectively, show a single large PCBM-rich core; the insertion of styrene units into the coil block of BCP100 is detrimental for the device efficiency, even if it produces an intermixed structure.

17.
Chemphyschem ; 11(3): 683-8, 2010 Feb 22.
Artículo en Inglés | MEDLINE | ID: mdl-20041455

RESUMEN

Dendronic antennae systems containing pyrene units as energy donors and a styrylpyridinium derivative as energy acceptor show efficient energy transfer from the green-emitting pyrene excimer to the red-emitting acceptor. For the third dendron generation the effective screening of the pyrene units on the acceptor provides thin films showing bright red emission. Single-layer light-emitting diodes prepared by properly balancing the dendrons and donor units concentration in polyvinylcarbazole show electroluminescence from the blue, green and red components of the monomeric donor, the donor excimer and the acceptor when excitons are generated in the polymer and subsequently transferred to the molecules by resonant energy transfer.

18.
Chem Sci ; 11(29): 7599-7608, 2020 Aug 07.
Artículo en Inglés | MEDLINE | ID: mdl-33033610

RESUMEN

The development of purely organic materials showing multicolor fluorescent and phosphorescent behaviour represents a formidable challenge in view of practical applications. Herein the rich photophysical behaviour of 3-(pyridin-2-yl)triimidazotriazine (TT-Py) organic molecule, comprising excitation-dependent fluorescence and phosphorescence under ambient conditions in both blended films and the crystalline phase, is investigated by means of steady state, time resolved and ultrafast spectroscopies and interpreted on the basis of X-ray diffraction studies and DFT/TDDFT calculations. In particular, by proper excitation wavelength, dual fluorescence and dual phosphorescence of molecular origin can be observed together with low energy phosphorescences resulting from aggregate species. It is demonstrated that the multiple emission properties originate from the copresence, in the investigated system, of an extended polycyclic nitrogen-rich moiety (TT), strongly rigidified by π-π stacking interactions and short C-H···N hydrogen bonds, and a fragment (Py) having partial conformational freedom.

19.
J Phys Chem Lett ; 11(20): 8893-8900, 2020 Oct 15.
Artículo en Inglés | MEDLINE | ID: mdl-32996314

RESUMEN

Emphasis was recently placed on the Cs2AgBiBr6 double perovskite as a possible candidate to substitute toxic lead in metal halide perovskites. However, its poor light-emissive features currently make it unsuitable for solid-state lighting. Lanthanide doping is an established strategy to implement luminescence in poorly emissive materials, with the additional advantage of fine-tuning the emission wavelength. We discuss here the impact of Eu and Yb doping on the optical properties of Cs2AgBiBr6 thin films, obtained from the solution processing of hydrothermally synthesized bulk crystalline powders, by combining experiments and density functional theory calculations. Eu(III) incorporation does not lead to the characteristic 5D0 → 7F2 emission feature at 2 eV, while only a weak trap-assisted sub-band gap radiative emission is reported. Oppositely, we demonstrate that incorporated Yb(III) leads to an intense and exclusive photoluminescence emission in the near-infrared as a result of the efficient sensitization of the lanthanide 2F5/2 → 2F7/2 transition.

20.
Chemphyschem ; 10(12): 2143-9, 2009 Aug 24.
Artículo en Inglés | MEDLINE | ID: mdl-19544493

RESUMEN

In order to understand the factors responsible for the improved efficiency and stability of organic light-emitting diodes (OLEDs) based on poly(9,9-dioctylfluorene) (PFO) when triphenylamine (TPA) is introduced as lateral fluorene substituent, we synthetize mono-disperse fluorene-thiophene oligomers as model compounds. Their blends with different concentrations of the fluorenone containing oligomer are studied in order to verify if only a reduction of ketonic defect sites or also an impeded energy transfer (ET) towards such sites are responsible for the suppression of the green emission band. We show that the introduction of TPA groups leads specifically both to an antioxidant action and a reduced ET towards residual defect sites, thanks to the environmental micro-encapsulation role played by TPA units surrounding the polymer backbone. As a result, the performances and colour stability of a device fabricated with TPA-substituted PFO (PFTPA) are strongly improved with respect to standard PFO device prepared in the same conditions.

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