From Static to Dynamic: Electron Density of HOMO at Biaryl Linkage Controls the Mechanism of Hole Delocalization

In order to extend the physical length of hole delocalization in a molecular wire, chromophores of increasing size are often desired. However, the effect of size on the efficacy and mechanism of hole delocalization remains elusive. Here, we employ a model set of biaryls to show that with increasing chromophore size, the mechanism of steady-state hole distribution switches from static delocalization in biaryls with smaller chromophores to dynamic hopping, as exemplified in the largest system, tBuHBC2 (i.e., “superbiphenyl”), which displays a vanishingly small electronic coupling. This important finding is analyzed with the aid of Hückel molecular orbital and Marcus–Hush theories. Our findings will enable the rational design of the novel molecular wires with length-invariant redox/optical properties suitable for long-range charge transfer

Absorptive capacity and performance in Malaysian SMEs / Zarina Denan

Many small and medium-sized enterprises (SMEs) presently evolve in a complex business environment characterized by globalization the internationalization of markets and the need for greater efficiency effectiveness and competitiveness based on innovation and knowledge. This has put increasing pressure upon the management of these firms especially manufacturing and technological SMEs that must now compete globally. Many entrepreneurial researches have highlighted the significance of potential strategies, technological innovation, or entrepreneurial orientation in improving SMEs productivity

Bimetallic Complexes Supported by a Redox-Active Ligand with Fused Pincer-Type Coordination Sites

The remarkable chemistry of mononuclear complexes featuring tridentate, meridionally chelating “pincer” ligands has stimulated the development of ligand frameworks containing multiple pincer sites. Here, the coordination chemistry of a novel pentadentate ligand (LN3O2) that provides two closely spaced NNO pincer-type compartments fused together at a central diarylamido unit is described. The trianionic LN3O2 chelate supports homobimetallic structures in which each M(II) ion (M = Co, Cu, Zn) is bound in a meridional fashion by the bridging diarylamido N atom and O,N-donors of the salicyaldimine arms. The metal centers are also coordinated by a mono- or bidentate auxiliary ligand (Laux), resulting in complexes with the general form [M2(LN3O2)(Laux)2]+ (where Laux = 1-methyl-benzimidazole (1MeBI), 2,2′-bipyridine (bpy), 4,4′-dibromo-2,2′-bipyridine (bpyBr2), or (S)-2-(4-isopropyl-4,5-dihydrooxazolyl)pyridine (S-iPrOxPy)). The fused nature of the NNO pincer sites results in short metal–metal distances ranging from 2.70 Å for [Co2(LN3O2) (bpy)2]+ to 3.28 Å for [Zn2(LN3O2) (bpy)2]+, as revealed by X-ray crystallography. The complexes possess C2 symmetry due to the twisting of the aryl rings of the μ-NAr2 core; spectroscopic studies indicate that chiral Laux ligands, such as S-iPrOxPy, are capable of controlling the helical sense of the LN3O2 scaffold. Since the four- or five-coordinate M(II) centers are linked solely by the amido moiety, each features an open coordination site in the intermetallic region, allowing for the possibility of metal–metal cooperativity in small-molecule activation. Indeed, the dicobalt(II) complex [Co2(LN3O2) (bpyBr2)2]+ reacts with O2 to yield a dicobalt(III) species with a μ-1,2-peroxo ligand. The bpy-containing complexes exhibit rich electrochemical properties due to multiple metal- and ligand-based redox events across a wide (3.0 V) potential window. Using electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT), it was determined that one-electron oxidation of [Co2(LN3O2) (bpy)2]+ results in formation of a S = 1/2 species with a LN3O2-based radical coupled to low-spin Co(II) centers

Research Methods for Visual Comfort Study

Research method in visual comfort area developed from a general to a more specific framework: from a consideration of window and lighting of office buildings in general to the specific daylight assessment of an experimental office. The investigation is divided into 4 parts: the survey-questionnaire, the field measurement, the subjective assessment under controlled daylight experiment and the advanced lighting calculation (computer simulation). This paper describes each method of data collection, the equipment used, and limitations

The acceptance of environmental friendly practices among smallholders in oil palm / Nurfidatul Denan

The environmental friendly practices is used to reduce or minimize the environmental pollutions and deforestation. The purpose of study is to assist acceptance level about environmental friendly practices in proper management. Besides, to evaluate the most factors (Knowledge, environment safety, good farm practices and ecosystem) between the acceptance levels environmental friendly practices among smallholders. The survey method is used for data collection and was distributed to 52 respondents that consists of smallholder in Gersik sub-division of Tangkak, Johor. The results were interpreted by hypothesis testing, descriptive analysis, Pearson correlation and Regression analysis by using Statistical Package for the Social Science (SPSS) version 22. The reliability test was checked using the Cronbach‟s Alpha and the value obtained was 0.808 that the survey can be proceed by distributing the questionnaire to the targeted respondents. After that, Pearson correlation analysis was carried out to determine the relationship between independent variables and dependent variable. There were very high relationship between all independent which with dependent variables, r = 0.805, 0.862, 0.887and 0.593 respectively. Meanwhile, the significance p value were 0.000 which less than 0.05, so null hypothesis (Ho) was rejected. Thus, it can be concluded that there positive significant relationship between independence variable and dependent variable. For result regression analysis, stated that the most influence variable toward the acceptance level environmental friendly practices is environment safety with the β= 0.593. From the model analysis, there are about 80.4% dependent variable was explained independent variable and 19.6% was explained by another factors. Conclusion, environmental friendly practices is one of suitable method to manage the farm in good management likes good drainage system, no open burning, correcting timing for harvesting and pruning and others activities. This is due to the concept of environment is nature and do not harmful to the human health. Not only that, it may increases the yield and productivity of the oil palm .Thus, the smallholders must apply the concept of environmental friendly practices in their plantation management

Synthesis of Homo- and Heterobimetallic Ni\u3csup\u3eII\u3c/sup\u3e–M\u3csup\u3eII\u3c/sup\u3e (M = Fe, Co, Ni, Zn) Complexes Based on an Unsymmetric Ligand Framework: Structures, Spectroscopic Features, and Redox Properties

Several homo- and heterobimetallic NiII–MII complexes (MII = Fe, Co, Ni, Zn) supported by an unsymmetric polydentate ligand (L13−) are reported (L13− is the trianion of 2-[bis(2-hydroxy-3,5-tert-butylphenyl)aminomethyl]-4-methyl-6-[(2-pyridylmethyl)iminomethyl]phenol). The L13− chelate provides two distinct coordination environments: a planar tridentate {N2O} site (A) and a tetradentate {NO3} site (B). Reaction of L13− with equimolar amounts of NiII and MII salts provides bimetallic complexes in which the NiII ion exclusively occupies the tetragonal A-site and the MII ion is found in the tripodal B-site. X-ray crystal structures revealed that the two metal centers are bridged by the central phenolate donor of L13− and an anionic X-ligand, where X = μ-1,1-acetate, hydroxide, or methoxide. The metal ions are separated by 3.0–3.1 Å in the MAMBX structures, where MA and MB indicate the ion located in the A and B sites, respectively, and X represents the second bridging ligand. Analysis of magnetic data and UV–Vis–NIR spectra indicate that, in all cases, the two metal ions adopt high-spin states in solution. The NiAII centers undergo one-electron reduction at −1.17 V vs. SCE, while the NiII and CoII ions in the phenolate-rich B-site are reduced at lower potentials. Significantly, the NiAII center possesses three open or labile coordination sites in a meridional geometry, which are generally occupied by solvent-derived ligands in the crystal structures. The NiMBX complexes serve as structural mimics of heterometallic Ni-containing sites in biology, such as the C-cluster of carbon monoxide dehydrogenase (CODH)

Ligand Frameworks for Transition-Metal Complexes That Model Metalloenzyme Active

Advances in the field of biomimetic inorganic chemistry require the design of sophisticated ligand frameworks that reflect the amazing complexity of metalloenzyme active sites. For instance, most active sites feature extensive hydrogen-bonding interactions between ligands bound to the metal center (the “first” coordination sphere) and nearby units in the outer (or “second”) sphere. Since these interactions modify the structural and electronic properties of the active sites, a number of inorganic chemists have sought to design ligands that permit outer-sphere functional groups to interact with first-sphere donors. This dissertation describes our contribution to these broader efforts to model the second coordination sphere. To date, our efforts have centered on the two classes of ligands based on second-sphere amide groups. The first set consists of 2,6-pyridinedicarboxamides with pendant pyridine or pyrimidine groups. Compared to the pincer ligands, the tripodal ligands posed a significantly greater synthetic challenge. We have succeeded in preparing a series of target ligands consisting of one, two, or three second-sphere heterocycles. My work has suggested that the second coordination sphere hydrogen bond interaction can be performed in our synthetic model. In addition, metalloenzymes with homobinuclear and heterobinuclear active sites play a central role in the chemistry of life. We have generated ligand scaffolds that support homo- and heterobimetallic complexes of relevance to metalloenzyme active sites. Firstly, the synthesis and coordination chemistry of a new asymmetric ligand designed to support nickel based heterobimetallic structures with relevance to bioinorganic chemistry is described. Additionally, we report the synthesis and coordination chemistry of ‘non-innocent’ pentadentate ligands intended to provide multiple sites for ligand-based oxidation and reduction. This ‘non-innocent’ ligand series contains a central diarylamido donor that serves as electron donor, in addition to ‘hard’ donor ligands (oxygen atoms), electron acceptor units, and ‘soft’ donor ligands. The resulting homobimetallic complexes (M = Co, Cu, and Zn) were characterized with X-ray crystallography and electrochemical methods. In addition, our studies found that the dicobalt(II) complex is a stable and efficient electrocatalyst for both H2 generation and H2O oxidation processes (i.e., water splitting)

Unraveling the Coulombic Forces in Electronically Decoupled Bichromophoric Systems during Two Successive Electron Transfers

Coulombic forces are vital in modulating the electron transfer dynamics in both synthetic and biological polychromophoric assemblies, yet quantitative studies of the impact of such forces are rare, as it is difficult to disentangle electrostatic forces from simple electronic coupling. To address this problem, the impact of Coulombic interactions in the successive removal of two electrons from a model set of spirobifluorenes, where the interchromophoric electronic coupling is nonexistent, is quantitatively assessed. By systematically varying the separation of the bifluorene moieties using model compounds, ion pairing, and solvation, these interactions, with energies up to about 0.4 V, are absent at distances greater than about 9 Å. These findings can be (quantitatively) applied for the design of polychromophoric assemblies, whereby the redox properties of donors and/or acceptors can be tuned by judicious positioning of the charged groups to control the electron‐transfer dynamics

A case study : academic achievement in an after-school tutoring program with Black middle school youth

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Energy Gap between the Poly-\u3cem\u3ep\u3c/em\u3e-phenylene Bridge and Donor Groups Controls the Hole Delocalization in Donor–Bridge–Donor Wires

Poly-p-phenylene wires are critically important as charge-transfer materials in photovoltaics. A comparative analysis of a series of poly-p-phenylene (RPPn) wires, capped with isoalkyl (iAPPn), alkoxy (ROPPn), and dialkylamino (R2NPPn) groups, shows unexpected evolution of oxidation potentials, i.e., decrease (−260 mV) for iAPPn, while increase for ROPPn (+100 mV) and R2NPPn (+350 mV) with increasing number of p-phenylenes. Moreover, redox/optical properties and DFT calculations of R2NPPn/R2NPPn+• further show that the symmetric bell-shaped hole distribution distorts and shifts toward one end of the molecule with only 4 p-phenylenes in R2NPPn+•, while shifting of the hole occurs with 6 and 8 p-phenylenes in ROPPn+• and iAPPn+•, respectively. Availability of accurate experimental data on highly electron-rich dialkylamino-capped R2NPPn together with ROPPn and iAPPn allowed us to demonstrate, using our recently developed Marcus-based multistate model (MSM), that an increase of oxidation potentials in R2NPPn arises due to an interplay between the electronic coupling (Hab) and energy difference between the end-capped groups and bridging phenylenes (Δε). A comparison of the three series of RPPn with varied Δε further demonstrates that decrease/increase/no change in oxidation energies of RPPn can be predicted based on the energy gap Δε and coupling Hab, i.e., decrease if Δε \u3c Hab (i.e., iAPPn), increase if Δε \u3e Hab (i.e., R2NPPn), and minimal change if Δε ≈ Hab (i.e., ROPPn). MSM also reproduces the switching of the nature of electronic transition in higher homologues of R2NPPn+• (n ≥ 4). These findings will aid in the development of improved models for charge-transfer dynamics in donor–bridge–acceptor systems