RESUMO

Novel four-coordinated boron complexes (1-5) were synthesized via a reaction between BF3·CH3OH and benzimidazole-phenolate ligands (L1-L5), which are N,O-donors. These complexes exhibit intense blue emission in the solution and solid states accompanied by notable fluorescence quantum yields (ΦF). The study of the structure-property relation, through theoretical and experimental approaches, revealed a distinctive trend where compounds incorporating electron-donating substituents (methyl and ethoxy groups) in the phenolate moiety manifest shifts in emission wavelengths across the blue spectrum, concomitant with an increase in ΦF. Furthermore, the incorporation of an aromatic ring into the benzimidazole moiety considerably intensifies the rate of radiative relaxation from excited states. Notably, in the solid phase, either as a crystalline powder or loaded into polymer films, these modified complexes maintain or even surpass ΦF values observed in molecular solutions, ranging from 0.18 to 0.57, depending on the substitution. This characteristic makes these compounds attractive for applications in optoelectronics. All of the compounds were characterized using 1H, 13C, 11B, and 19F NMR, elemental analysis, and the molecular structures were corroborated through single-crystal X-ray diffraction analysis. Computational calculations via time-dependent density functional theory further elucidate the tunability of optical bandgaps through group substitution on ligands, aligning well with experimental observations.

RESUMO

Scorpions are a mesodiverse and nocturnal group of arachnids inhabiting most biomes worldwide. Different species of scorpions have divergent adaptations to the substrate they live in, but most of them share an intriguing characteristic: their exoskeleton contains fluorophores that emit blue-greenish fluorescence under ultraviolet radiation. Although there are some reports in the literature on the study of fluorescence in scorpions, the biological functionality of this light emission is currently unknown and is under debate. In this work, the properties of emission from the scorpion's exoskeleton are studied by means of digitally processed photographs taken of living specimens under ultraviolet illumination and complemented with standard spectroscopic measurements of emission and excitation spectra. With the aim of identifying possible correlations between the fluorescence, the characteristics color of the exoskeleton and the biology of the scorpions, 4 families, 9 genera and 24 species were studied. Our results suggest that the intensity of fluorescence is heterogeneous throughout the scorpion's exoskeleton studied here in such a way that pedipalps and metasomal segments fluoresce more intensely than the mesosomal segments. The spectrum of fluorescence across species is practically identical, suggesting that the same fluorophores are present in their exoskeletons. However, the fluorescence intensity emitted by each species varies according to their characteristic color (associated with the exoskeleton optical reflectance). Since the coloration of the exoskeleton is determined by the concentration of melanin and other pigments according to the substrate where scorpions live in, we conclude by suggesting that fluorescence may correlate directly to the ecomorphotype of the scorpions.

Assuntos

RESUMO

Light emission properties of a fluorene cross-conjugated polymer (PF⁻1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF⁻1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF⁻1, two different electron injectors, poly [(9,9-bis(3'-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9⁻dioctylfluorene)] (PFN) and lithium fluoride (LiF), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage (Von) of approximately 4.5 V and a luminance maximum of 878 cd/m² at 5.5 V, with a current density of 20 A/m². For the lasing properties of PF⁻1, we found a lasing threshold of around 75 µJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye.

RESUMO

Our group previously reported the synthesis of four polythiophene derivatives (P1-P4) used for solar cells. The cells were prepared under room conditions by spin coating, leading to low efficiencies. However, after the addition of 6-nitro-3-(E)-3-(4-dimethylaminophenyl)allylidene)-2,3-dihydrobenzo[d]-[1,3,2] oxazaborole (M1) to their active layers, the efficiencies of the cells showed approximately a two-fold improvement. In this paper, we study this enhancement mechanism by performing ultrafast transient absorption (TA) experiments on the active layer of the different cells. Our samples consisted of thin films of a mixture of PC61BM with the polythiophenes derivatives P1-P4. We prepared two versions of each sample, one including the molecule M1 and another without it. The TA data suggests that the efficiency improvement after addition of M1 is due not only to an extended absorption spectrum towards the infrared region causing a larger population of excitons but also to the possible creation of additional channels for transport of excitons and/or electrons to the PC61BM interface.

RESUMO

In this work the two-photon activity of nanoparticles obtained from a fluorene monomer (M1) and its cross-conjugated polymer (P1) is reported. Aqueous suspensions of M1 and P1 nanoparticles prepared through the reprecipitation method exhibited maximum two-photon absorption (TPA) cross-sections of 84 and 9860 GM (1 GM = 10(-50) cm(4) s) at 740 nm, respectively, and a fluorescence quantum yield of ~1. Such a two-photon activity was practically equal with respect to that for molecular solutions of M1 and P1. These materials were then successfully encapsulated into silica nanoparticles to provide bio-compatibly. A lung cancer cell line (A549) and a human cervical cancer cell line (HeLa cells) were incubated with our fluorescent silica nanoparticles to carry out two-photon imaging. By means of these studies we demonstrate that optimized nonlinear optical polymers loaded in silica nanoparticles can be used as efficient probes with low cytotoxicity and good photostability for two-photon fluorescence microscopy. To the best of our knowledge, studies concerning polymer-doped silica nanoparticles exhibiting large two-photon activity have not been reported in the literature.

Assuntos

RESUMO

Macroscopic single crystals of (E)-5-(diethylamino)-2-((3,5-dinitrophenylimino)methyl)phenol (DNP) were obtained from slow cooling of chloroform or dichlorometane saturated solutions at controlled temperature. X-ray diffraction analysis showed that this compound crystallizes in a noncentrosymmetric space group (P2(1)2(1)2(1)). Thermal analysis was performed and indicated that the crystals are stable until 260 °C. Second-order nonlinear optical properties of DNP were experimentally investigated in solution through EFISH technique and in solid state through the Kurtz-Perry powder technique. Crystals of compound DNP exhibited a second-harmonic signals 39 times larger than of the technologically useful potassium dihydrogenphosphate (KDP) under excitation at infrared wavelengths. In addition, the second-order nonlinear optical properties of DNP were also studied at visible wavelengths through the photorefractive effect and applied to demonstrate dynamic holographic reconstruction.

Assuntos

RESUMO

We synthesized three novel highly fluorescent compounds, 2-(2'-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile, 2-(3"-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile, and 2-(4-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile by Knoevenagel condensation. The first two were synthesized without solvent in the presence of piperidine as a catalyst; the third was synthesized without a catalyst and with N,N-dimethylformamide as a solvent. In solution, the molar absorption coefficients showed absorptions at 380, 378, and 396 nm, respectively; in solid state, absorptions were at 398, 390, and 442 nm, respectively. The fluorescence emission was at 540, 540 and 604 nm, respectively, the 2-(4-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile showed a red shift in the emission of 64 nm compared to the other two compounds. The fluorescence quantum yield for the compounds in powder form showed values of 0.05, 0.14, and 0.006, respectively; compared with the value measured for the Alq3 reference, 2-(3"-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile had a lightly higher value. The third harmonic generation measurement for 2-(2'-pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile yielded a χ(3) value of 5.5 × 10-12 esu, similar to that reported for commercial polymers.

RESUMO

Dendrons with ferrocenyl ended groups joined by styryl moieties were attached to a porphyrin core. All the dendrons used for dendrimer synthesis showed trans configuration. The chemical structure of the first generation dendron was confirmed by X-ray crystallographic studies. The structure of the synthesized dendrimers was confirmed by 1H- and 13C-NMR, electrospray mass spectrometry and elemental analysis. Cubic non-linear optical behavior of the ferrocene and porphyrin-containing dendrimers was studied in solid thin films by THG Maker-Fringe technique at 1,260 nm.

Assuntos