Fine-Tuning LUMO Energy Levels of Conjugated Polymers Containing a B←N Unit

The LUMO and HOMO energy levels (<i>E</i>_LUMO/<i>E</i>_HOMO) are key parameters for conjugated polymers, which can greatly affect their applications in organic opto-electronic devices. In this manuscript, with donor–acceptor (D–A) type conjugated polymers based on double B←N bridged bipyridine (BNBP) unit, we report fine-tuning of <i>E</i>_LUMO of conjugated polymers in a wide range via substitutions on both D unit and A unit. We synthesize eight D–A type conjugated polymers with alternating electron-deficient BNBP unit and electron-rich bithiophene (BT) unit in the main chain. By changing the substitutes on BNBP or BT, the <i>E</i>_LUMO of these polymers can be finely tuned in a wide range from −3.3 eV to −3.7 eV. We comprehensively investigate the electronic structures, photophysical properties, charge-transporting properties and polymer solar cell (PSC) device applications of these polymers. In PSC devices, these BNBP-based polymers can be used either as electron donors (with high-lying <i>E</i>_LUMO/<i>E</i>_HOMO) or as electron acceptors (with low-lying <i>E</i>_LUMO/<i>E</i>_HOMO). The PSC device with the BNBP-based polymer donor exhibits a PCE of 2.92% and the PSC device with the BNBP-based polymer acceptor exhibits a PCE of 5.16%. These results indicate a new approach to modulate the LUMO energy levels of D–A type conjugated polymers by modifications on both D unit and A unit

White Electroluminescence from All-Phosphorescent Single Polymers on a Fluorinated Poly(arylene ether phosphine oxide) Backbone Simultaneously Grafted with Blue and Yellow Phosphors

On the basis of a fluorinated poly­(arylene ether phosphine oxide) backbone with both high triplet energy and appropriate HOMO/LUMO levels, highly efficient all-phosphorescent single white-emitting polymers were designed and successfully synthesized via a “two-step addition” strategy. Simultaneous blue and yellow triplet emissions were achieved to generate white electroluminescence with a promising luminous efficiency as high as 18.4 cd/A (8.5 lm/W, 7.1%) and CIE coordinates of (0.31, 0.43)

Highly Efficient Phosphorescent Furo[3,2‑<i>c</i>]pyridine Based Iridium Complexes with Tunable Emission Colors over the Whole Visible Range

A series of highly efficient phosphorescent Ir complexes with tunable emission colors over the whole visible range have been designed and synthesized based on furo­[3,2-<i>c</i>]­pyridine ligand. By mainly varying the molecular structures of the C-chelated blocks, the emission maxima of these complexes can be obviously tailored from 477 to 641 nm while keeping the considerable photoluminescence quantum yields (PLQYs) (0.55–0.78 at wavelength of 475–560 nm and 0.10–0.34 at wavelength of 590–640 nm). Correspondingly, the phosphorescent organic light-emitting diodes (OLEDs) achieve high-performance greenish-blue, green, greenish-yellow, orange, red, and deep-red electrophosphorescence, revealing state-of-art external quantum efficiences (EQEs) of 20.0% (46.6 cd/A), 31.8% (89.0 cd/A), 19.9% (71.9 cd/A), 16.6% (38.9 cd/A), 12.0% (16.7 cd/A), and 8.5% (7.3 cd/A) as well as Commision Internationale de L’Eclairage (CIE) coordinates of (0.25, 0.48), (0.30, 0.58), (0.43, 0.54), (0.62, 0.37), (0.66, 0.32), and (0.70, 0.29), respectively. The results clearly demonstrate the great potential of furo­[3,2-<i>c</i>]­pyridine based phosphors used for full-color OLED displays

Forms of phosphorus in Cerrado\'s Oxisol as function of agricultural usage time

Não há dúvidas que a exitosa exploração do Cerrado só foi possível graças às pesquisas que desenvolveram tecnologias de correção e adubação específicas para esse ambiente. Apesar de estar consolidado como um dos principais ambientes de produção agropecuária do mundo, as pesquisas devem avançar contribuindo, cada vez mais, com aumento na eficiência do uso do fósforo (P), por ser o elemento mais limitante para produção agrícola nesse ambiente. Devido às características dos solos dessa região, parte do P aplicado é retido pelo solo em formas que as plantas não conseguem absorver, resultando na acumulação de quantidades significativas do nutriente no solo. Apesar de não ser um assunto relativamente novo e do grande número de trabalhos, o tema avaliação da disponibilidade de fósforo do solo ainda provoca dúvidas. Além dos estudos em que é avaliada a eficiência de diversos extratores como Mehlich-1 e resina de troca aniônica, outras técnicas passaram a ser utilizadas para esse fim. Estudos objetivando avaliar a distribuição (dinâmica) do fósforo nas diferentes frações do solo e as mudanças nessa distribuição em função do manejo aplicado aos cultivos e, também, do tempo de cultivo, têm sido conduzidos com crescente intensidade. Estudos também têm sido conduzidos buscando identificar as formas de acumulação de P no solo. Para isso, modernas técnicas espectroscópicas, como por exemplo, a espectroscopia baseada em luz synchrotron, têm sido utilizadas como uma poderosa ferramenta, auxiliando na identificação dos compostos presentes no solo. Face ao exposto, objetivou-se avaliar as alterações no fósforo disponível e nas frações e formas de fósforo em solo de Cerrado submetido ao manejo em semeadura direta com diferentes tempos de cultivo. Foram coletadas amostras compostas em quatro áreas que se encontravam no momento da coleta com 5, 8, 12 e 18 anos de cultivo desde a abertura das áreas, e também numa área sob vegetação nativa. O fósforo disponível foi extraído por Mehlich-1 e resina de troca aniônica. As amostras foram submetidas ao fracionamento químico de fósforo e espectroscopia de alta resolução da borda de absorção (XANES - X-ray absorption near edge structure). Observou-se que, de maneira geral, os teores de fósforo no solo foram sempre mais altos nas áreas cultivadas, principalmente na camada superficial, em comparação aos da área com vegetação nativa, o que reflete o impacto das adubações fosfatadas. A aplicação superficial do fertilizante fosfatado gerou nítidos gradientes de P no perfil do solo, principalmente para as frações lábeis e moderadamente lábeis, sendo essas frações as que sofreram maior influência do fertilizante quando comparadas às frações de menor disponibilidade. Considerando-se os mesmos extratores, os teores das frações orgânicas foram maiores em comparação às correspondentes frações inorgânicas. As formas de fósforo nos solos estudados foram predominantemente associadas ao alumínio e ao ferro, com destaque para o nutriente associado ao alumínio, sendo que, com o ferro, a associação ocorreu predominantemente por meio de fenômenos de adsorção em detrimento de fenômenos de precipitação.There is no doubt that the successful exploitation of the Cerrado was only possible due to the research that developed specific correction and fertilization technologies to this particular environment. Due to the characteristics of soils in the region, part of applied phosphorus (P) is retained by the soil in plant unavailable forms, resulting in accumulation of significant amounts of nutrient in the soil. Despite not being a relatively new issue and the large number of research performed on this topic, the assessment of the soil P availability still raise important questions. In addition to studies in which the efficiency of various extractants have been tested, such as Mehlich-1 and anion exchange resin, other techniques are being used for this purpose. Studies for evaluating the P distribution (dynamic) in different soil fractions and the changes in this fractions due to the management applied to crops and also the time of cultivation have been conducted with increasing intensity. Studies have also been carried out in order to identify the forms of P accumulation in soils. For this purpose, modern spectroscopic techniques such as spectroscopy based on synchrotron light source, have been used as a powerful tool, assisting in the identification of P compounds presents in the soil. The aims of this study were to evaluate the changes in available, fractions and forms of P in soils of Cerrado with different times under no-till cultivation system. Composite soil samples were collected in four areas under 5, 8, 12 and 18 years of no-till cultivation since the areas were opened, and also in a area under native vegetation. The soil in the area was classified as Typic Hapludox and the areas were cultivated alternating crops of soybeans, corn and cotton. Available P was extracted by Mehlich - 1 and anion exchange resin. The samples were subjected to Hedley´s chemical fractionation of P and X- ray absorption near edge structure (XANES). It was observed that, in general, the levels of P in the soil were always higher in cultivated areas, mainly in the topsoil, when compared to the area under native vegetation, which reflects the impact of phosphate fertilization. Surface application of phosphate fertilizer produced sharp gradients of P in the soil profile, especially for both labile and moderately labile fractions, and these fractions suffered the greatest influence of fertilizer compared to fractions of lower availability. Considering the same extractants, the organic P fractions contents were higher compared to the corresponding inorganic fractions. Forms of phosphorus in soils were predominantly associated with aluminum (Al) and iron (Fe), especially P associated with Al, and with Fe the association occurred predominantly through adsorption phenomenon rather than precipitation reactions

Enhancing Lead Passivation in Contaminated Soil: Impacts of the Chemical Modification of Oxygen-Containing Groups (OCGs) on the Surface of Hydrochar

In this study, we selected walnut shell-derived pristine HC (pHC) and two modified derivatives obtained by oxidative and alkali treatments (designated mHC-O and mHC-A, respectively) to investigate the passivation performance of Pb(II) in contaminated soil. The yields of mHC-A and mHC-O were 70.58% and 95.38%, respectively, after posttreatment. According to the XPS, FTIR, and acidity titration results, the amounts of the three major OCGs (i.e. C−O, C=O, and O−C=O) all increased after H2O2 oxidation. Moreover, chemical modification fundamentally changed the structural characteristics of pHC. DTPA extraction tests indicated that the extractable Pb content after 30 days of incubation decreased by 13.60%, 19.32% and 14.53% at 7% (w/w) doses of HC, mHC-O and mHC-A, respectively, compared to that of the control. Furthermore, mHC-O was superior to pHC and mHC-A in terms of Pb passivation efficiency, which was consistent with the results of BCR sequential extraction and leaching tests using three root exudates. For mHC-O at the 7% dose, the contents of bioavailable Pb in the contaminated soil were 19.85 and 8.83 mg/kg based on DTPA leaching and BCR analysis, respectively, while they were 0.616, 0.564 and 0.07 mg/kg in the root exudate leaching tests of Ophiopogon japonicus, radish and spinach, respectively, indicating that the root exudate leaching method lowered the bioavailable Pb content compared to the DTPA and BCR methods. Overall, Oxidation posttreatment with HC could improve the passivation of Pb in contaminated soils.</p

Phosphonate-Functionalized Donor Polymer as an Underlying Interlayer To Improve Active Layer Morphology in Polymer Solar Cells

A novel polymer is developed and used as underlying interlayer to improve donor polymer/acceptor material blend morphology of active layer in polymer solar cells (PSCs). The polymer poly­{<i>N</i>-9-[1,17-bis­(diethylphosphonate)­heptadecanyl]-2,7-carbazole-<i>alt</i>-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)} (PCDTBT-Pho) is designed by attaching polar phosphonate moieties to the side chain of the donor polymer, poly­[<i>N</i>-9-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT). The pendant phosphonate moieties lead to different solubility and proper surface energy of PCDTBT-Pho. As a result, in PSC devices, the underlying PCDTBT-Pho layer facilitates the formation of biscontinuous network morphology in the active layer, makes the donor polymer enriched at the anode side, and induces the donor polymer to crystallize. These improvements contribute to improved charge separation and transport, leading to short-circuit current density enhancement by 12% and power conversion efficiency enhancement by 8% of the PSC devices. Thus, the design and application of PCDTBT-Pho indicate a novel approach to optimize active layer morphology and improve photovoltaic efficiency of PSCs

Blue Thermally Activated Delayed Fluorescence Polymers with Nonconjugated Backbone and Through-Space Charge Transfer Effect

We demonstrate novel molecular design for thermally activated delayed fluorescence (TADF) polymers based on a nonconjugated polyethylene backbone with through-space charge transfer effect between pendant electron donor (D) and acceptor (A) units. Different from conventional conjugated D–A polymers with through-bond charge transfer effect, the nonconjugated architecture avoids direct conjugation between D and A units, enabling blue emission. Meanwhile, spatial π–π interaction between the physically separated D and A units results in both small singlet–triplet energy splitting (0.019 eV) and high photoluminescence quantum yield (up to 60% in film state). The resulting polymer with 5 mol % acceptor unit gives efficient blue electroluminescence with Commission Internationale de l’Eclairage coordinates of (0.176, 0.269), together with a high external quantum efficiency of 12.1% and low efficiency roll-off of 4.9% (at 1000 cd m^–2), which represents the first example of blue TADF nonconjugated polymer

Facile Preparation of Molybdenum Bronzes as an Efficient Hole Extraction Layer in Organic Photovoltaics

We proposed a facile and green one-pot strategy to synthesize Mo bronzes nanoparticles to serve as an efficient hole extraction layer in polymer solar cells. Mo bronzes were obtained through reducing the fractional self-aggregated ammonium heptamolybdate with appropriate reducing agent ascorbic acid, and its optoelectronic properties were fully characterized. The synthesized Mo bronzes displayed strong n-type semiconductor characteristics with a work function of 5.2–5.4 eV, matched well with the energy levels of current donor polymers. The presented gap states of the Mo bronzes near the Fermi level were beneficial for facilitating charge extraction. The as-synthesized Mo bronzes were used as hole extraction layer in polymer solar cells and significantly enhanced the photovoltaic performance and stability. The power conversion efficiency was increased by more than 18% compared with the polyethylene dioxythiophene:polystyrenesulfonate-based reference cell. The excellent performance and facile preparation render the as-synthesized solution-processed Mo bronzes nanoparticles a promising candidate for hole extraction layer in low-cost and efficient polymer solar cells

Rationally Designed Surfactants for Few-Layered Graphene Exfoliation: Ionic Groups Attached to Electron-Deficient π‑Conjugated Unit through Alkyl Spacers

Mass production of graphene with low cost and high throughput is very important for practical applications of graphene materials. The most promising approach to produce graphene with low defect content at a large scale is exfoliation of graphite in an aqueous solution of surfactants. Herein, we report a molecular design strategy to develop surfactants by attaching ionic groups to an electron-deficient π-conjugated unit with flexible alkyl spacers. The molecular design strategy enables the surfactant molecules to interact strongly with both the graphene sheets and the water molecules, greatly improving graphene dispersion in water. As the result, a few-layered graphene concentration as high as 1.2–5.0 mg mL^–1 is demonstrated with the surfactant, which is much higher than those (<0.1 mg mL^–1) obtained with normal aromatic or nonaromatic surfactants. Moreover, the surfactant can be easily synthesized at large scale. The superior performance and convenient synthesis make the surfactant very promising for mass production of graphene

Poly(spirobifluorene)s Containing Nonconjugated Diphenylsulfone Moiety: Toward Blue Emission Through a Weak Charge Transfer Effect

Instead of conjugated dibenzothiophene-<i>S,S</i>-dioxide (DBTSO), we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-deficient unit into the main chain of poly­(spirobifluorene)­s (PSFs). Because of the weaker electron affinity of DPSO relative to DBTSO, the charge transfer from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be effectively prevented. Consequently, the resultant polymers containing DPSO moiety show pure blue emissions, which is different from DBTSO-based PSFs that exhibit undesired green emissions. With a single-layer device configuration, a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130 cd/m² have been realized for the polymer PSFDPSO03. The corresponding CIE coordinates are (0.17, 0.18), nearly independent of the applied current density from 2 to 592 mA/cm². These results indicate that tuning the electron affinity of the incorporated electron-deficient units is a very promising strategy to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability