Search

Though increasing attention is being paid to adolescents' social media use, racially/ethnically-marginalized youth remain under-represented in that literature, and the effect of social media and its mechanism on these youth remain unclear. This study examined the effects of social media use on Black and Hispanic youth's psychological and academic functioning, with an attempt to investigate the role of online racial discrimination in accounting for these associations. Participants consisted of 356 Black and Hispanic youth (M

While studies on youth's purpose have flourished in the last two decades, the work was mostly cross-sectional and derived from Western settings. This research examined the developmental trajectories of purpose exploration and commitment of Taiwanese youth during middle adolescence, with a focus on how they associate with youth's psychological functioning in terms of life satisfaction and depressive symptoms and whether social support moderates such development. A total of 369 vocational high school students in Taiwan (45% females; M

Introduction Whereas evidence has shown that a sense of purpose is linked to optimal adjustment, longitudinal work investigating the development of purpose identification as well as its effect on psychological functioning among non-Western samples during adolescence is needed. Methods Three hundred and eighty-seven senior high school students (253 female, 65.37%; mean age = 15.76 years at the first investigation) from Taiwan completed surveys four times beginning in the fall of tenth grade and ending in the spring of eleventh grade with a six-month interval. Using self-ratings, purpose identification was evaluated in all four assessments and psychological functioning was examined through life satisfaction and depressive symptoms in the first and the last survey. Results Growth curve analyses revealed an increased slope in purpose identification over the first two years of high school, and such a trajectory was similar across boys and girls. Additionally, increases in purpose identification predicted enhanced life satisfaction and reduced depressive symptoms among both boys and girls. There was only one gender difference: The negative association between purpose identification trajectory and depressive symptoms was stronger for girls than for boys. Conclusions There is an increase in the development of identified purpose during middle adolescence among high school students in Taiwan. Such change not only promotes life satisfaction in adolescents but is also preventive of adolescent depression. As such, the current findings highlight the significance for adolescents to discover and commit to a purpose.

Drawing on the information processing model for the development of aggression, children's acquisition of aggressive responses could be associated with parenting that communicated norms favoring aggression. Extending this view, the present study examined the mediating role of children's normative beliefs about relational aggression (NBRA) on the association between psychologically controlling parenting and children's relational aggression (RA), and further explored whether this possible indirect effect would be contingent on the child's gender. 341 upper elementary school students (174 boys and 166 girls) reported perceived paternal psychological control (PPC) and maternal psychological control (MPC) during their fifth-grade fall semester, rated their NBRA during their sixth-grade fall semester, and assessed RA through a peer-nomination procedure during their sixth-grade spring semester. Results demonstrated that the indirect effects of perceived PPC and MPC on children's RA

Little is known about why American youth tend to have higher self-esteem than do Chinese youth. This research examined the role of psychologically controlling parenting during early adolescence. 825 youth (48% females; Mage = 12.73 years) in the United States and China reported on their self-esteem and parents’ psychological control every 6 months from the fall of 7th grade to spring of 8th grade. Both American and Chinese youth’s self-esteem decreased over time, but American youth consistently had higher self-esteem. American parents were less psychologically controlling than were Chinese parents who, unlike American parents, became more psychologically controlling over time. These differences in psychologically controlling parenting contributed to the tendency for American youth to have higher self-esteem than their Chinese counterparts.

The development, optimization, and assessment of new methods for the preparation of conjugated materials is key to the continued progress of organic electronics. Direct C–H activation methods have emerged and developed over the last 10 years to become an invaluable synthetic tool for the preparation of conjugated polymers for both redox-active and solid-state applications. Here, we evaluate direct (hetero)arylation polymerization (DHAP) methods for the synthesis of indaceno[1,2-b:5,6-b′]dithiophene-based polymers. We demonstrate, using a range of techniques, including direct visualization of individual polymer chains via high-resolution scanning tunneling microscopy, that DHAP can produce polymers with a high degree of regularity and purity that subsequently perform in organic thin-film transistors comparably to those made by other cross-coupling polymerizations that require increased synthetic complexity. Ultimately, this work results in an improved atom economy by reducing the number of synthetic steps to access high-performance molecular and polymeric materials.

Three thiophene ring-terminated benzothieno[3,2-b]benzothiophene (BTBT) derivatives, C-C6-DBTTT, C-C12-DBTTT, and L-C12-DBTTT, were designed and synthesized, differing in the isomerization of alkyl...

A novel fused heterocycle-flanked diketopyrrolopyrrole (DPP) monomer, thieno[2,3-b]pyridine diketopyrrolopyrrole (TPDPP), was designed and synthesized. When copolymerized with 3,4-difluorothiophene using Stille coupling polymerization, the new polymer pTPDPP-TF possesses a highly planar conjugated polymer backbone due to the fused thieno[2,3-b]pyridine flanking unit that effectively alleviates the steric hindrance with both the central DPP core and the 3,4-difluorothiophene repeat unit. This new polymer exhibits a high electron affinity (EA) of −4.1 eV and was successfully utilized as an n-type polymer semiconductor for applications in organic field-effect transistors (OFETs) and all polymer solar cells. A promising n-type charge carrier mobility of 0.1 cm2 V–1 s–1 was obtained in bottom-contact, top-gate OFETs, and a power conversion efficiency (PCE) of 2.72% with a high open-circuit voltage (VOC) of 1.04 V was achieved for all polymer solar cells using PTB7-Th as the polymer donor.

Two donor–acceptor conjugated polymers with azaisoindigo as acceptor units and bithiophene and terthiophene as donor units have been synthesized by Stille polymerization. These two polymers have been successfully applied in field-effect transistors and polymer solar cells. By changing the donor component of the conjugated polymer backbone from bithiophene to terthiophene, the density of thiophene in the backbone is increased, manifesting as a decrease in both ionization potential and in electron affinity. Therefore, the charge transport in field-effect transistors switches from ambipolar to predominantly hole transport behavior. PAIIDTT exhibits hole mobility up to 0.40 cm2/Vs and electron mobility of 0.02 cm2/Vs, whereas PAIIDTTT exhibits hole mobility of 0.62 cm2/Vs. Polymer solar cells were fabricated based on these two polymers as donors with PC61BM and PC71BM as acceptor where PAIIDTT shows a modest efficiency of 2.57% with a very low energy loss of 0.55 eV, while PAIIDTTT shows a higher efficiency of 6.16% with a higher energy loss of 0.74 eV. Our results suggest that azaisoindgo is a useful building block for the development of efficient polymer solar cells with further improvement possibility by tuning the alternative units on the polymer backbone. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2691–2699.

Nine pBCNx polymers based on a donor–π-acceptor benzo[1,2-b:4,5-b′]dithiophene-(E)-2,3-di(thiophen-2-yl)acrylonitrile main-chain structure and n-octyl/2-ethylhexyl as the side-chain substituents have been designed and synthesized. The thermochromism of the pBCNx polymers has been carefully examined in both solution and the thin-film state. With additional evidences from Raman spectroscopy and AFM microscopy, we have deciphered the varied colours of nine pBCNx polymers in solution and the pronounced thin-film thermochromism only observed for certain pBCNx polymers, i.e., pBCN4, pBCN5, pBCN6, and pBCN8. The alkyl side-chain, and hence the solubility or aggregation of pBCNx polymers, is a main factor of the varied colour in solution and the varied thermochromism in the thin film. We have identified that a stronger main-chain and main-chain interaction are present on the (E)-2,3-di(thiophen-2-yl)acrylonitrile moiety, whereas the poor to moderate solubility pBCN3, pBCN5′, and pBCN7 exhibit pronounced thermochromism in solution, and pBCN4, pBCN5, pBCN6, and pBCN8 are four polymers which have good solubility in solution and show thermochromism in the thin-film state. We took navy blue pBCN3 (poor solubility), magenta pBCN4 (good solubility), and reddish purple pBCN5′ (moderate solubility) for the fabrication of bulk heterojunction organic photovoltaics (OPVs). With a solvent annealing treatment, the power conversion efficiency of the OPVs has been improved significantly from 4.7% to 6.2% for the good solubility pBCN4, but there is little and no improvement for the moderate solubility pBCN5′ and poor solubility pBCN3, respectively. Our study verifies that the good OPV performance of the pBCNx polymers can be correlated to the pronounced thin-film thermochromism. A good solubility of the polymer is a common characteristic of a material with significant thin-film thermochromism and good OPV performance.

Two new alternating copolymers, PAIIDBT and PAIIDSe have been prepared by incorporating a highly electron deficient azaisoindigo core. The molecular structure and packing of the monomer is determined from the single crystal X-ray diffraction. Both polymers exhibit high EAs and highly planar polymer backbones. When polymers are used as the semiconducting channel for solution-processed thin film transistor application, good properties are observed. A–A type PAIIDBT exhibits unipolar electron mobility as high as 1.0 cm2 V−1 s−1, D–A type PAIIDSe exhibits ambipolar charge transport behavior with predominately electron mobility up to 0.5 cm2 V−1 s−1 and hole mobility to 0.2 cm2 V−1 s−1. The robustness of the extracted mobility values are also commented on in detail. Molecular orientation, thin film morphology and energetic disorder of both polymers are systematically investigated.

Conspectus The active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging. The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address these limitations, providing tunable absorption with high extinction coefficients, thus contributing to device photocurrent. The ability to vary and optimize the lowest unoccupied molecular orbital (LUMO) energy level for a specific donor polymer is also an important requirement, ensuring minimal energy loss on electron transfer and as high an internal voltage as possible. Initially perylene diimide acceptors were evaluated as promising acceptor materials. These electron deficient aromatic molecules can exhibit good electron transport, facilitated by close packed herringbone crystal motifs, and their energy levels can be synthetically tuned. The principal drawback of this class of materials, their tendency to crystallize on too large a length scale for an optimal heterojunction nanostructure, has been shown to be overcome through introduction of conformation twisting through steric effects. This has been primarily achieved by coupling two units together, forming dimers with a large intramolecular twist, which suppresses both nucleation and crystal growth. The generic design concept of rotationally symmetrical aromatic small molecules with extended π orbital delocalization, including polyaromatic hydrocarbons, phthalocyanines, etc., has also provided some excellent small molecule acceptors. In most cases, additional electron withdrawing functionality, such as imide or ester groups, can be incorporated to stabilize the LUMO and improve properties. New calamitic acceptors have been developed, where molecular orbital hybridization of electron rich and poor segments can be judiciously employed to precisely control energy levels. Conformation and intermolecular associations can be controlled by peripheral functionalization leading to optimization of crystallization length scales. In particular, the use of rhodanine end groups, coupled electronically through short bridged aromatic chains, has been a successful strategy, with promising device efficiencies attributed to high lying LUMO energy levels and subsequently large open circuit voltages.

A novel photoactive polymer with two different molecular weights is reported, based on a new building block: thieno[3,2-b][1]benzothiophene isoindigo. Due to the improved crystallinity, optimal blend morphology, and higher charge mobility, solar-cell devices of the high-molecular-weight polymer exhibit a superior performance, affording efficiencies of 9.1% without the need for additives, annealing, or additional extraction layers during device fabrication.

An all carbon non-fullerene electron acceptor material based on diindeno[1,2-g:1′,2′-s]rubicene (DIR) was readily synthesized and processed for bulk-heterojunction organic solar cells. High PCE up to 3.05% with a relatively high VOC of 1.22 V has been achieved with P3HT electron donor material by the variation of donor–acceptor blending ratio.

A series of new 9,10-diphenylanthracene-based, 2,6-linked blue-light-emitting copolymers bearing hole- or electron-transporter as well as bulky substituent were successfully synthesized. Photophysical, thermal, electrochemical, and electroluminescence (EL) properties of these copolymers were studied and characterized. Bright and efficient blue fluorescence in the solid state was achieved by incorporating bulky substituent into the copolymer backbone. Both hole- and electron-transport-substituted copolymers apparently enhanced the electroluminescent performance of their polymeric light-emitting diodes (PLEDs). A diphenylvinyl-bearing copolymer (pDPV) PLED exhibited sky-blue EL (λmaxEL = 473 nm, CIEx,y = 0.16, 0.28) with peak luminous efficiency of 2.21 cd/A; a N-carbazole bearing copolymer (pCBZ) PLED displayed a blue EL (λmaxEL = 469 nm, CIEx,y = 0.15, 0.22) with peak luminous efficiency of 2.15 cd/A. OXD-7 (1,3-bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl)benzene) as an electron-transporting dopant wa...

All non-dopant white organic light-emitting diodes (WOLEDs) have been realized by using solid state highly fluorescent red bis(4-( N -(1-naphthyl)phenylamino)phenyl)fumaronitrile ( NPAFN ) and amorphous bipolar blue light-emitting 2-(4-diphenylamino)phenyl-5-(4-triphenylsilyl)phenyl-1,3,4-oxadiazole ( TPAOXD ), together with well known green fluorophore tris(8-hydroxyquinolinato)aluminum ( Alq 3 ). The fabrication of multilayer WOLEDs did not involve the hard-to-control doping process. Two WOLEDs, Device B and C, different in layer thickness of Alq 3 , 30 and 15 nm, respectively, emitted strong electroluminescence (EL) as intense as 25,000 cd/m 2 . For practical solid state lighting application, EL intensity exceeding 1000 cd/m 2 was achieved at current density of 18–19 mA/cm 2 or driving voltage of 6.5–8 V and the devices exhibited external quantum efficiency ( η ext ) of 2.6–2.9% corresponding to power efficiency ( η P ) of 2.1–2.3 lm/W at the required brightness. The thickness of Alq 3 layer is decisive in color quality of non-dopant WOLEDs. The Commission Internationale de l’Eclairage (CIE) coordinates of fairly white EL of Device B varied only little from (0.34, 0.39) to (0.34, 0.38) at driving voltage between 6 and 14 V. Device B exhibited relatively high color rendering indexes (CRIs) in the range of 74–81, which were essentially voltage-independent. The other WOLED, Device C, showed even better color purity of white EL (CIE x , y = 0.34, 0.31) along with higher CRI of 83 at 8 V, although higher voltage deteriorated the color quality of WOLED.

Brunner's gland adenomas are rare, benign, duodenal tumors that occur in middle age. These lesions are often discovered accidentally during upper gastrointestinal (UGI) endoscopy or can sometimes manifest as UGI bleeding or duodenal obstruction. The definite diagnosis is determined by histology. We report a case of Brunner's gland adenoma presenting with UGI bleeding and epigastralgia. UGI endoscopy revealed a giant polypoid mass about 4–5 cm in diameter with a central shallow ulcer in the duodenal bulb. Endoscopic ultrasonography (EUS) revealed a mixed echoic, pedunculated mass arising from the submucosa or mucosa with an intact muscle layer and several cystic lesions within the mass. The patient underwent surgical excision of the tumor and recovered without sequelae. We suggest that the multiple cystic changes in a heterogeneous mixed echoic mass are the key EUS features of Brunner's gland adenoma. EUS plays an important role in the diagnosis of Brunner's gland adenoma before histologic confirmation of the resected tumor.

A newly synthesized benzo(1,2-b:4,5-b')dithiophene-based low band-gap copolymer pBCN is amenable to solvent annealing in the fabrication of organic photovoltaics, of which power conversion efficiency is greatly improved to 4.2% with PC(61)BM or 4.9% with PC(71)BM.

We report a novel solution-processable high molecule iridium complex, bis[5-methyl-7-trifluoro methyl-5H-enzo(c)(1,5)naphthyridin-6-one]iridium(picolinate) (CF3BNO), that exhibits a relatively short excited-state lifetime (0.30 μs) and extremely high quantum yield (95%). Current efficiency of 89.1 cd A−1 at 100 cd m−2 was obtained by using the CF3BNO complex to fabricate a blue-green light-emitting device.

Long life-time molecular-based organic electronics, such as organic light-emitting diodes (OLEDs), organic solar cells, or organic transistors etc, inevitably demand their constituent molecules to be highly thermal-stable. Coupling with special needs in molecular design, the resultant increasing molecular weight (MW) will eventually make the molecules difficult to deposit if via dry-process, while using wet-process would frequently result in undesired relatively poorer efficiency. Surprisingly, two high-molecule composing OLEDs with relatively high-efficiency were obtained by using solution-process. A blue OLED with a blue dye doped in a novel high-MW, wide band-gap host, 3,5-di(9Hcarbazol-9-yl) tetraphenylsilane (SimCP2), yielded 24 lm/W (38 cd/A) at 100 nits, and a green OLED using a novel high-MW green dye, bis[5-methyl-7-trifluoromethyl-5H–benzo (c)(1,5) naphthyridin-6-one] iridium (picolinate) (CF3BNO), yielded 70 lm/W (89 cd/A), while their dry-processed blue and green counterparts yield 1.7 and 21 lm/W, respectively. Importantly, although the comparatively high MW has made the resulting molecules extremely difficult to vacuum-evaporate and has resulted in poor device performance, the wet-process has been proven effective in fabricating two high molecule-containing OLEDs with relatively high efficiency. The successful demonstration suggests that the same approach may as well be extended to other organic devices that compose or should compose high molecules.

One of the two possible regioisomers can be exclusively formed by combining a suitable solvent and a specific amount of triethylamine as a base during the amination of allyl bromide 5. The S N 2' product 7 was produced using dichloromethane as a solvent and triethylamine (7 equiv) as base; S N 2 product 6 was predominantly generated in hexane with 0.5 equivalents of triethylamine. Furthermore, a new reaction condition for the efficient cyclization of 7 to yield α-methylene p-lactam 8 using Sn[N(TMS) 2 ] 2 as a reagent, is disclosed.

We report a detailed comparison of absorption spectroscopy, electrochemistry, DFT calculations, field-effect charge mobility, as well as organic photovoltaic characteristics between thiophene- and selenophene-bridged donor–acceptor low-band-gap copolymers. In these copolymers, a significant reduction of the band-gap energy was observed for selenophene-bridged copolymers by UV-visible absorption spectroscopy and cyclic voltammetry. Field-effect charge mobility studies reveal that the enhanced hole mobility of the selenophene-bridged copolymers hinges on the solubilising alkyl side chain of the copolymers. Both cyclic voltammetry experiments and theoretical calculations showed that the decreased band-gap energy is mainly due to the lowering of the LUMO energy level, and the raising of the HOMO energy level is just a secondary cause. These results are reflected in a significant increase of the short circuit current density (JSC) but a slight decrease of the open circuit voltage (VOC) of their bulk-heterojunction organic photovoltaics (BHJ OPVs), of which the electron donor materials are a selenophene-bridged donor–acceptor copolymer: poly{9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl) benzo[c][1,2,5]-thiadiazole} (pCzSe) or poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-b′]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(selenophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTSe), or a thiophene-bridged donor–acceptor copolymer: poly{9-dodecyl-9H-carbazole-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pCzS) or poly{4,8-bis(2-ethylhexyloxy)benzo[1,2-b;4,5-b′]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (pBDTS); the electron acceptor material is [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Judging from our device data, the potential Se–Se interactions of the selenophene-bridged donor–acceptor copolymers, which is presumably beneficial for the fill factor (FF) of BHJ OPVs, is rather susceptible to the device fabrication conditions.